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2021. március 18.

AA21-077A: Detecting Post-Compromise Threat Activity Using the CHIRP IOC Detection Tool

Original release date: March 18, 2021
Summary

This Alert announces the CISA Hunt and Incident Response Program (CHIRP) tool. CHIRP is a forensics collection tool that CISA developed to help network defenders find indicators of compromise (IOCs) associated with activity detailed in the following CISA Alerts:

Similar to Sparrow—which scans for signs of APT compromise within an M365 or Azure environment—CHIRP scans for signs of APT compromise within an on-premises environment.

In this release, CHIRP, by default, searches for IOCs associated with malicious activity detailed in AA20-352A and AA21-008A that has spilled into an on-premises enterprise environment.

CHIRP is freely available on the CISA GitHub Repository. Note: CISA will continue to release plugins and IOC packages for new threats via the CISA GitHub Repository.

CISA advises organizations to use CHIRP to:

  • Examine Windows event logs for artifacts associated with this activity;
  • Examine Windows Registry for evidence of intrusion;
  • Query Windows network artifacts; and
  • Apply YARA rules to detect malware, backdoors, or implants.

Network defenders should review and confirm any post-compromise threat activity detected by the tool. CISA has provided confidence scores for each IOC and YARA rule included with CHIRP’s release. For confirmed positive hits, CISA recommends collecting a forensic image of the relevant system(s) and conducting a forensic analysis on the system(s).

If an organization does not have the capability to follow the guidance in this Alert, consider soliciting third-party IT security support. Note: Responding to confirmed positive hits is essential to evict an adversary from a compromised network.

Click here for a PDF version of this report.

Technical DetailsHow CHIRP Works

CHIRP is a command-line executable with a dynamic plugin and indicator system to search for signs of compromise. CHIRP has plugins to search through event logs and registry keys and run YARA rules to scan for signs of APT tactics, techniques, and procedures. CHIRP also has a YAML file that contains a list of IOCs that CISA associates with the malware and APT activity detailed in CISA Alerts AA20-352A and AA21-008A.

Currently, the tool looks for:

  • The presence of malware identified by security researchers as TEARDROP and RAINDROP;
  • Credential dumping certificate pulls;
  • Certain persistence mechanisms identified as associated with this campaign;
  • System, network, and M365 enumeration; and
  • Known observable indicators of lateral movement.

Network defenders can follow step-by-step instructions on the CISA CHIRP GitHub repository to add additional IOCs, YARA rules, or plugins to CHIRP to search for post-compromise threat activity related to the SolarWinds Orion supply chain compromise or new threat activity.

Compatibility

CHIRP currently only scans Windows operating systems.

Instructions

CHIRP is available on CISA’s GitHub repository in two forms:

  1. A compiled executable

  2. A python script

CISA recommends using the compiled version to easily scan a system for APT activity. For instructions to run, read the README.md in the CHIRP GitHub repository.

If you choose to use the native Python version, see the detailed instructions on the CHIRP GitHub repository.

MitigationsInterpreting the Results

CHIRP provides results of its scan in JSON format. CISA encourages uploading the results into a security information and event management (SIEM) system, if available. If no SIEM system is available, results can be viewed in a compatible web browser or text editor. If CHIRP detects any post-compromise threat activity, those detections should be reviewed and confirmed. CISA has provided confidence scores for each IOC and YARA rule included with CHIRP’s release. For confirmed positive hits, CISA recommends collecting a forensic image of the relevant system(s) and conducting a forensic analysis on the system(s).

If you do not have the capability to follow the guidance in this Alert, consider soliciting third-party IT security support. Note: Responding to confirmed positive hits is essential to evict an adversary from a compromised network.

Frequently Asked Questions
  1. What systems should CHIRP run on?

    Systems running SolarWinds Orion or believed to be involved in any resulting lateral movement.

  2. What should I do with results?

    Ingest the JSON results into a SIEM system, web browser, or text editor.

  3. Are there existing tools that CHIRP complements and/or provide the same benefit as CHIRP?
    1. Antivirus software developers may have begun to roll out detections for the SolarWinds post-compromise activity. However, those products can miss historical signs of compromise. CHIRP can provide a complementary benefit to antivirus when run.

    2. CISA previously released the Sparrow tool that scans for APT activity within M365 and Azure environments related to activity detailed in CISA Alerts AA20-352A and AA21-008A. CHIRP provides a complementary capability to Sparrow by scanning for on-premises systems for similar activity.

  4. How often should I run CHIRP?

    CHIRP can be run once or routinely. Currently, CHIRP does not provide a mechanism to run repeatedly in its native format.

  5. Do I need to configure the tool before I run it?

    No.

  6. Will CHIRP change or affect anything on the system(s) it runs on?

    No, CHIRP only scans the system(s) it runs on and makes no active changes.

  7. How long will it take to run CHIRP?

    CHIRP will complete its scan in approximately 1 to 2 hours. Duration will be dependent on the level of activity, the system, and the size of the resident data sets. CHIRP will provide periodic progress updates as it runs.

  8. If I have questions, who do I contact?  

    For general questions regarding CHIRP, please contact CISA via email at central@cisa.dhs.gov or by phone at 1-888-282-0870. For reporting indicators of potential compromise, contact us by submitting a report through our website at https://us-cert.cisa.gov/report. For all technical issues or support for CHIRP, please submit issues at the CISA CHIRP GitHub Repository

Revisions
  • March 18, 2021: Initial Publication

This product is provided subject to this Notification and this Privacy & Use policy.

2021. március 17.

AA21-076A: TrickBot Malware

Original release date: March 17, 2021
Summary

This Advisory uses the MITRE Adversarial Tactics, Techniques, and Common Knowledge (ATT&CK®) framework. See the ATT&CK for Enterprise for all referenced threat actor tactics and techniques.

The Cybersecurity and Infrastructure Security Agency (CISA) and Federal Bureau of Investigation (FBI) have observed continued targeting through spearphishing campaigns using TrickBot malware in North America. A sophisticated group of cybercrime actors is luring victims, via phishing emails, with a traffic infringement phishing scheme to download TrickBot.

TrickBot—first identified in 2016—is a Trojan developed and operated by a sophisticated group of cybercrime actors. Originally designed as a banking Trojan to steal financial data, TrickBot has evolved into highly modular, multi-stage malware that provides its operators a full suite of tools to conduct a myriad of illegal cyber activities.

To secure against TrickBot, CISA and FBI recommend implementing the mitigation measures described in this Joint Cybersecurity Advisory, which include blocking suspicious Internet Protocol addresses, using antivirus software, and providing social engineering and phishing training to employees.

Click here for a PDF version of this report.

Technical Details

TrickBot is an advanced Trojan that malicious actors spread primarily by spearphishing campaigns using tailored emails that contain malicious attachments or links, which—if enabled—execute malware (Phishing: Spearphishing Attachment [T1566.001], Phishing: Spearphishing Link [T1566.002]). CISA and FBI are aware of recent attacks that use phishing emails, claiming to contain proof of a traffic violation, to steal sensitive information. The phishing emails contain links that redirect to a website hosted on a compromised server that prompts the victim to click on photo proof of their traffic violation. In clicking the photo, the victim unknowingly downloads a malicious JavaScript file that, when opened, automatically communicates with the malicious actor’s command and control (C2) server to download TrickBot to the victim’s system.

Attackers can use TrickBot to:

  • Drop other malware, such as Ryuk and Conti ransomware, or
  • Serve as an Emotet downloader.[1]

TrickBot uses person-in-the-browser attacks to steal information, such as login credentials (Man in the Browser [T1185]). Additionally, some of TrickBot’s modules spread the malware laterally across a network by abusing the Server Message Block (SMB) Protocol. TrickBot operators have a toolset capable of spanning the entirety of the MITRE ATT&CK framework, from actively or passively gathering information that can be used to support targeting (Reconnaissance [TA0043]), to trying to manipulate, interrupt, or destroy systems and data (Impact [TA0040]).

TrickBot is capable of data exfiltration, cryptomining, and host enumeration (e.g., reconnaissance of Unified Extensible Firmware Interface or Basic Input/Output System [UEFI/BIOS] firmware).[2] For host enumeration, operators deliver TrickBot in modules containing a configuration file with specific tasks.

Figure 1 lays out TrickBot’s use of enterprise techniques.

Figure 1: MITRE ATT&CK enterprise techniques used by TrickBot

 

MITRE ATT&CK Techniques

According to MITRE, TrickBot [S0266] uses the ATT&CK techniques listed in table 1.

Table 1: TrickBot ATT&CK techniques for enterprise

Initial Access [TA0001]

Technique Title

ID Use Phishing: Spearphishing Attachment T1566.001 TrickBot has used an email with an Excel sheet containing a malicious macro to deploy the malware. Phishing: Spearphishing Link T1566.002

TrickBot has been delivered via malicious links in phishing emails.

Execution [TA0002]

Technique Title ID Use Scheduled Task/Job: Scheduled Task T1053.005 TrickBot creates a scheduled task on the system that provides persistence. Command and Scripting Interpreter: Windows Command Shell T1059.003 TrickBot has used macros in Excel documents to download and deploy the malware on the user’s machine. Native API T1106 TrickBot uses the Windows Application Programming Interface (API) call, CreateProcessW(), to manage execution flow. User Execution: Malicious Link T1204.001 TrickBot has sent spearphishing emails in an attempt to lure users to click on a malicious link. User Execution: Malicious File T1204.002 TrickBot has attempted to get users to launch malicious documents to deliver its payload.

Persistence [TA0003]

Technique Title ID Use Scheduled Task/Job: Scheduled Task T1053.005 TrickBot creates a scheduled task on the system that provides persistence. Create or Modify System Process: Windows Service T1543.003 TrickBot establishes persistence by creating an autostart service that allows it to run whenever the machine boots.

Privilege Escalation [TA0004]

Technique Title ID Use Scheduled Task/Job: Scheduled Task T1053.005 TrickBot creates a scheduled task on the system that provides persistence. Process Injection: Process Hollowing T1055.012 TrickBot injects into the svchost.exe process. Create or Modify System Process: Windows Service T1543.003 TrickBot establishes persistence by creating an autostart service that allows it to run whenever the machine boots.

 Defense Evasion [TA0005]

Technique Title ID Use Obfuscated Files or Information T1027 TrickBot uses non-descriptive names to hide functionality and uses an AES CBC (256 bits) encryption algorithm for its loader and configuration files. Obfuscated Files or Information: Software Packing T1027.002 TrickBot leverages a custom packer to obfuscate its functionality. Masquerading T1036 The TrickBot downloader has used an icon to appear as a Microsoft Word document. Process Injection: Process Hollowing T1055.012 TrickBot injects into the svchost.exe process. Modify Registry T1112 TrickBot can modify registry entries. Deobfuscate/Decode Files or Information T1140 TrickBot decodes the configuration data and modules. Subvert Trust Controls: Code Signing T1553.002 TrickBot has come with a signed downloader component. Impair Defenses: Disable or Modify Tools T1562.001 TrickBot can disable Windows Defender.

Credential Access [TA0006]

Technique Title ID Use Input Capture: Credential API Hooking T1056.004 TrickBot has the ability to capture Remote Desktop Protocol credentials by capturing the CredEnumerateA API. Unsecured Credentials: Credentials in Files T1552.001 TrickBot can obtain passwords stored in files from several applications such as Outlook, Filezilla, OpenSSH, OpenVPN and WinSCP. Additionally, it searches for the .vnc.lnk affix to steal VNC credentials. Unsecured Credentials: Credentials in Registry T1552.002 TrickBot has retrieved PuTTY credentials by querying the Software\SimonTatham\Putty\Sessions registry key. Credentials from Password Stores T1555 TrickBot can steal passwords from the KeePass open-source password manager. Credentials from Password Stores: Credentials from Web Browsers T1555.003 TrickBot can obtain passwords stored in files from web browsers such as Chrome, Firefox, Internet Explorer, and Microsoft Edge, sometimes using esentutl.

Discovery [TA0007]

Technique Tactic ID Use System Service Discovery T1007 TrickBot collects a list of install programs and services on the system’s machine. System Network Configuration Discovery T1016 TrickBot obtains the IP address, location, and other relevant network information from the victim’s machine. Remote System Discovery T1018 TrickBot can enumerate computers and network devices. System Owner/User Discovery T1033 TrickBot can identify the user and groups the user belongs to on a compromised host. Permission Groups Discovery T1069 TrickBot can identify the groups the user on a compromised host belongs to. System Information Discovery T1082 TrickBot gathers the OS version, machine name, CPU type, amount of RAM available from the victim’s machine. File and Directory Discovery T1083 TrickBot searches the system for all of the following file extensions: .avi, .mov, .mkv, .mpeg, .mpeg4, .mp4, .mp3, .wav, .ogg, .jpeg, .jpg, .png, .bmp, .gif, .tiff, .ico, .xlsx, and .zip. It can also obtain browsing history, cookies, and plug-in information. Account Discovery: Local Account T1087.001 TrickBot collects the users of the system. Account Discovery: Email Account T1087.003 TrickBot collects email addresses from Outlook. Domain Trust Discovery T1482 TrickBot can gather information about domain trusts by utilizing Nltest.

Collection [TA0009]

Technique Tactic ID Use Data from Local System T1005 TrickBot collects local files and information from the victim’s local machine. Input Capture:Credential API Hooking T1056.004 TrickBot has the ability to capture Remote Desktop Protocol credentials by capturing the CredEnumerateA API. Person in the Browser T1185 TrickBot uses web injects and browser redirection to trick the user into providing their login credentials on a fake or modified webpage.

Command and Control [TA0011]

Technique Tactic ID Use Fallback Channels T1008 TrickBot can use secondary command and control (C2) servers for communication after establishing connectivity and relaying victim information to primary C2 servers. Application Layer Protocol: Web Protocols T1071.001 TrickBot uses HTTPS to communicate with its C2 servers, to get malware updates, modules that perform most of the malware logic and various configuration files. Ingress Tool Transfer T1105 TrickBot downloads several additional files and saves them to the victim's machine. Data Encoding: Standard Encoding T1132.001 TrickBot can Base64-encode C2 commands. Non-Standard Port T1571 Some TrickBot samples have used HTTP over ports 447 and 8082 for C2. Encrypted Channel: Symmetric Cryptography T1573.001 TrickBot uses a custom crypter leveraging Microsoft’s CryptoAPI to encrypt C2 traffic.

Exfiltration [TA0010]

Technique Tactic ID Use Exfiltration Over C2 Channel T1041 TrickBot can send information about the compromised host to a hardcoded C2 server. Detection Signatures

CISA developed the following snort signature for use in detecting network activity associated with TrickBot activity.

 

alert tcp any [443,447] -> any any (msg:"TRICKBOT:SSL/TLS Server X.509 Cert Field contains 'example.com' (Hex)"; sid:1; rev:1; flow:established,from_server; ssl_state:server_hello; content:"|0b|example.com"; fast_pattern:only; content:"Global Security"; content:"IT Department"; pcre:"/(?:\x09\x00\xc0\xb9\x3b\x93\x72\xa3\xf6\xd2|\x00\xe2\x08\xff\xfb\x7b\x53\x76\x3d)/"; classtype:bad-unknown; metadata:service ssl,service and-ports;)

 

alert tcp any any -> any $HTTP_PORTS (msg:"TRICKBOT_ANCHOR:HTTP URI GET contains '/anchor'"; sid:1; rev:1; flow:established,to_server; content:"/anchor"; http_uri; fast_pattern:only; content:"GET"; nocase; http_method; pcre:"/^\/anchor_?.{3}\/[\w_-]+\.[A-F0-9]+\/?$/U"; classtype:bad-unknown; priority:1; metadata:service http;)

 

alert tcp any $SSL_PORTS -> any any (msg:"TRICKBOT:SSL/TLS Server X.509 Cert Field contains 'C=XX, L=Default City, O=Default Company Ltd'"; sid:1; rev:1; flow:established,from_server; ssl_state:server_hello; content:"|31 0b 30 09 06 03 55 04 06 13 02|XX"; nocase; content:"|31 15 30 13 06 03 55 04 07 13 0c|Default City"; nocase; content:"|31 1c 30 1a 06 03 55 04 0a 13 13|Default Company Ltd"; nocase; content:!"|31 0c 30 0a 06 03 55 04 03|"; classtype:bad-unknown; reference:url,www.virustotal.com/gui/file/e9600404ecc42cf86d38deedef94068db39b7a0fd06b3b8fb2d8a3c7002b650e/detection; metadata:service ssl;)

 

alert tcp any any -> any $HTTP_PORTS (msg:"TRICKBOT:HTTP Client Header contains 'boundary=Arasfjasu7'"; sid:1; rev:1; flow:established,to_server; content:"boundary=Arasfjasu7|0d 0a|"; http_header; content:"name=|22|proclist|22|"; http_header; content:!"Referer"; content:!"Accept"; content:"POST"; http_method; classtype:bad-unknown; metadata:service http;)

 

alert tcp any any -> any $HTTP_PORTS (msg:"TRICKBOT:HTTP Client Header contains 'User-Agent|3a 20|WinHTTP loader/1.'"; sid:1; rev:1; flow:established,to_server; content:"User-Agent|3a 20|WinHTTP loader/1."; http_header; fast_pattern:only; content:".png|20|HTTP/1."; pcre:"/^Host\x3a\x20(?:\d{1,3}\.){3}\d{1,3}(?:\x3a\d{2,5})?$/mH"; content:!"Accept"; http_header; content:!"Referer|3a 20|"; http_header; classtype:bad-unknown; metadata:service http;)

 

alert tcp any $HTTP_PORTS -> any any (msg:"TRICKBOT:HTTP Server Header contains 'Server|3a 20|Cowboy'"; sid:1; rev:1; flow:established,from_server; content:"200"; http_stat_code; content:"Server|3a 20|Cowboy|0d 0a|"; http_header; fast_pattern; content:"content-length|3a 20|3|0d 0a|"; http_header; file_data; content:"/1/"; depth:3; isdataat:!1,relative; classtype:bad-unknown; metadata:service http;)

 

alert tcp any any -> any $HTTP_PORTS (msg:"TRICKBOT:HTTP URI POST contains C2 Exfil"; sid:1; rev:1; flow:established,to_server; content:"Content-Type|3a 20|multipart/form-data|3b 20|boundary=------Boundary"; http_header; fast_pattern; content:"User-Agent|3a 20|"; http_header; distance:0; content:"Content-Length|3a 20|"; http_header; distance:0; content:"POST"; http_method; pcre:"/^\/[a-z]{3}\d{3}\/.+?\.[A-F0-9]{32}\/\d{1,3}\//U"; pcre:"/^Host\x3a\x20(?:\d{1,3}\.){3}\d{1,3}$/mH"; content:!"Referer|3a|"; http_header; classtype:bad-unknown; metadata:service http;)

 

alert tcp any any -> any $HTTP_PORTS (msg:"HTTP URI GET/POST contains '/56evcxv' (Trickbot)"; sid:1; rev:1; flow:established,to_server; content:"/56evcxv"; http_uri; fast_pattern:only; classtype:bad-unknown; metadata:service http;)

 

alert icmp any any -> any any (msg:"TRICKBOT_ICMP_ANCHOR:ICMP traffic conatins 'hanc'"; sid:1; rev:1; itype:8; content:"hanc"; offset:4; fast_pattern; classtype:bad-unknown;)

 

alert tcp any any -> any $HTTP_PORTS (msg:"HTTP Client Header contains POST with 'host|3a 20|*.onion.link' and 'data=' (Trickbot/Princess Ransomeware)"; sid:1; rev:1; flow:established,to_server; content:"POST"; nocase; http_method; content:"host|3a 20|"; http_header; content:".onion.link"; nocase; http_header; distance:0; within:47; fast_pattern; file_data; content:"data="; distance:0; within:5; classtype:bad-unknown; metadata:service http;)

 

alert tcp any any -> any $HTTP_PORTS (msg:"HTTP Client Header contains 'host|3a 20|tpsci.com' (trickbot)"; sid:1; rev:1; flow:established,to_server; content:"host|3a 20|tpsci.com"; http_header; fast_pattern:only; classtype:bad-unknown; metadata:service http;) Mitigations

CISA and FBI recommend that network defenders—in federal, state, local, tribal, territorial governments, and the private sector—consider applying the following best practices to strengthen the security posture of their organization's systems. System owners and administrators should review any configuration changes prior to implementation to avoid negative impacts.

  • Provide social engineering and phishing training to employees.
  • Consider drafting or updating a policy addressing suspicious emails  that specifies users must report all suspicious emails to the security and/or IT departments.
  • Mark external emails with a banner denoting the email is from an external source to assist users in detecting spoofed emails.
  • Implement Group Policy Object and firewall rules.
  • Implement an antivirus program and a formalized patch management process.
  • Implement filters at the email gateway and block suspicious IP addresses at the firewall.
  • Adhere to the principle of least privilege.
  • Implement a Domain-Based Message Authentication, Reporting & Conformance validation system.
  • Segment and segregate networks and functions.
  • Limit unnecessary lateral communications between network hoses, segments and devices.
  • Consider using application allowlisting technology on all assets to ensure that only authorized software executes, and all unauthorized software is blocked from executing on assets. Ensure that such technology only allows authorized, digitally signed scripts to run on a system.
  • Enforce multi-factor authentication.
  • Enable a firewall on agency workstations configured to deny unsolicited connection requests.
  • Disable unnecessary services on agency workstations and servers.
  • Implement an Intrusion Detection System, if not already used, to detect C2 activity and other potentially malicious network activity
  • Monitor web traffic. Restrict user access to suspicious or risky sites.
  • Maintain situational awareness of the latest threats and implement appropriate access control lists.
  • Disable the use of SMBv1 across the network and require at least SMBv2 to harden systems against network propagation modules used by TrickBot.
  • Visit the MITRE ATT&CK Techniques pages (linked in table 1 above) for additional mitigation and detection strategies.
  • See CISA’s Alert on Technical Approaches to Uncovering and Remediating Malicious Activity for more information on addressing potential incidents and applying best practice incident response procedures.

For additional information on malware incident prevention and handling, see the National Institute of Standards and Technology Special Publication 800-83, Guide to Malware Incident Prevention and Handling for Desktops and Laptops.

Resources References Revisions
  • March 17, 2021: Initial Version

This product is provided subject to this Notification and this Privacy & Use policy.

2021. március 3.

AA21-062A: Mitigate Microsoft Exchange Server Vulnerabilities

Original release date: March 3, 2021
Summary

Cybersecurity and Infrastructure Security (CISA) partners have observed active exploitation of vulnerabilities in Microsoft Exchange Server products. Successful exploitation of these vulnerabilities allows an unauthenticated attacker to execute arbitrary code on vulnerable Exchange Servers, enabling the attacker to gain persistent system access, as well as access to files and mailboxes on the server and to credentials stored on that system. Successful exploitation may additionally enable the attacker to compromise trust and identity in a vulnerable network. Microsoft released out-of-band patches to address vulnerabilities in Microsoft Exchange Server. The vulnerabilities impact on-premises Microsoft Exchange Servers and are not known to impact Exchange Online or Microsoft 365 (formerly O365) cloud email services.

This Alert includes both tactics, techniques and procedures (TTPs) and the indicators of compromise (IOCs) associated with this malicious activity. To secure against this threat, CISA recommends organizations examine their systems for the TTPs and use the IOCs to detect any malicious activity. If an organization discovers exploitation activity, they should assume network identity compromise and follow incident response procedures. If an organization finds no activity, they should apply available patches immediately and implement the mitigations in this Alert.

Click here for IOCs in STIX format.

Technical Details

Microsoft has released out-of-band security updates to address four vulnerabilities in Exchange Server:

  • CVE-2021-26855 allows an unauthenticated attacker to send arbitrary HTTP requests and authenticate as the Exchange Server. The vulnerability exploits the Exchange Control Panel (ECP) via a Server-Side Request Forgery (SSRF). This would also allow the attacker to gain access to mailboxes and read sensitive information.
  • CVE-2021-26857, CVE-2021-26858, and CVE-2021-27065 allow for remote code execution.  
    • CVE-2021-26858 and CVE-2021-27065 are similar post-authentication arbitrary write file vulnerabilities in Exchange. An attacker, authenticated either by using CVE-2021-26855 or via stolen admin credentials, could write a file to any path on the server.

    • CVE-2021-26857 is an insecure deserialization vulnerability in the Unified Messaging service. An attacker, authenticated either by using CVE-2021-26855 or via stolen admin credentials, could execute arbitrary code as SYSTEM on the Exchange Server.

  • To locate a possible compromise of these CVEs, we encourage you to read the Microsoft Advisory.

It is possible for an attacker, once authenticated to the Exchange server, to gain access to the Active Directory environment and download the Active Directory Database.

Tactics, Techniques and Procedures

The majority of the TTPs in this section are sourced from a blog post from Volexity, a third party cybersecurity firm. Note: the United States Government does not endorse any commercial product or service, including any subjects of analysis. Any reference to specific commercial products, processes, or services by service mark, trademark, manufacturer, or otherwise, does not constitute or imply their endorsement, recommendation, or favoring by the United States Government.

Volexity has observed the following files as targets of HTTP POST requests:

  • /owa/auth/Current/themes/resources/logon.css
  • /owa/auth/Current/themes/resources/owafont_ja.css
  • /owa/auth/Current/themes/resources/lgnbotl.gif
  • /owa/auth/Current/themes/resources/owafont_ko.css
  • /owa/auth/Current/themes/resources/SegoeUI-SemiBold.eot
  • /owa/auth/Current/themes/resources/SegoeUI-SemiLight.ttf
  • /owa/auth/Current/themes/resources/lgnbotl.gif

Administrators should search the ECP server logs for the following string (or something similar):

S:CMD=Set-OabVirtualDirectory.ExternalUrl='

The logs can be found at <exchange install path>\Logging\ECP\Server\.

To determine possible webshell activity, administrators should search for aspx files in the following paths:

  • \inetpub\wwwroot\aspnet_client\ (any .aspx file under this folder or sub folders)
  • \<exchange install path>\FrontEnd\HttpProxy\ecp\auth\ (any file besides TimeoutLogoff.aspx)
  • \<exchange install path>\FrontEnd\HttpProxy\owa\auth\ (any file or modified file that is not part of a standard install)
  • \<exchange install path>\FrontEnd\HttpProxy\owa\auth\Current\ (any aspx file in this folder or subfolders)
  • \<exchange install path>\FrontEnd\HttpProxy\owa\auth\<folder with version number>\ (any aspx file in this folder or subfolders)

Administrators should search in the /owa/auth/Current directory for the following non-standard web log user-agents. These agents may be useful for incident responders to look at to determine if further investigation is necessary.

These should not be taken as definitive IOCs:

  • DuckDuckBot/1.0;+(+http://duckduckgo.com/duckduckbot.html)
  • facebookexternalhit/1.1+(+http://www.facebook.com/externalhit_uatext.php)
  • Mozilla/5.0+(compatible;+Baiduspider/2.0;++http://www.baidu.com/search/spider.html)
  • Mozilla/5.0+(compatible;+Bingbot/2.0;++http://www.bing.com/bingbot.htm)
  • Mozilla/5.0+(compatible;+Googlebot/2.1;++http://www.google.com/bot.html
  • Mozilla/5.0+(compatible;+Konqueror/3.5;+Linux)+KHTML/3.5.5+(like+Gecko)+(Exabot-Thumbnails)
  • Mozilla/5.0+(compatible;+Yahoo!+Slurp;+http://help.yahoo.com/help/us/ysearch/slurp)
  • Mozilla/5.0+(compatible;+YandexBot/3.0;++http://yandex.com/bots)
  • Mozilla/5.0+(X11;+Linux+x86_64)+AppleWebKit/537.36+(KHTML,+like+Gecko)+Chrome/51.0.2704.103+Safari/537.36

Volexity observed these user-agents in conjunction with exploitation to /ecp/ URLs:

  • ExchangeServicesClient/0.0.0.0
  • python-requests/2.19.1
  • python-requests/2.25.1

These user-agents were also observed having connections to post-exploitation web-shell access:

  • antSword/v2.1
  • Googlebot/2.1+(+http://www.googlebot.com/bot.html)
  • Mozilla/5.0+(compatible;+Baiduspider/2.0;++http://www.baidu.com/search/spider.html)

As with the non-standard user-agents, responders can examine internet information services (IIS) logs from Exchange Servers to identify possible historical activity. Also, as with the non-standard user agents, these should not be taken as definitive IOCs:

  • POST /owa/auth/Current/
  • POST /ecp/default.flt
  • POST /ecp/main.css
  • POST /ecp/<single char>.js

Volexity has seen attackers leverage the following IP addresses. Although these are tied to virtual private servers (VPSs) servers and virtual private networks (VPNs), responders should investigate these IP addresses on their networks and act accordingly:

  • 103.77.192[.]219
  • 104.140.114[.]110
  • 104.250.191[.]110
  • 108.61.246[.]56
  • 149.28.14[.]163
  • 157.230.221[.]198
  • 167.99.168[.]251
  • 185.250.151[.]72
  • 192.81.208[.]169
  • 203.160.69[.]66
  • 211.56.98[.]146
  • 5.254.43[.]18
  • 5.2.69[.]14
  • 80.92.205[.]81
  • 91.192.103[.]43

Volexity has also provided the following YARA signatures that can be run within your network to assist in finding signs of a compromise.


rule webshell_aspx_simpleseesharp : Webshell Unclassified
{
    meta:
        author = “threatintel@volexity.com”
        date = “2021-03-01”
        description = “A simple ASPX Webshell that allows an attacker to write further files to disk.”
        hash = “893cd3583b49cb706b3e55ecb2ed0757b977a21f5c72e041392d1256f31166e2”
 
    strings:
        $header = “<%@ Page Language=\”C#\” %>”
        $body = “<% HttpPostedFile thisFile = Request.Files[0];thisFile.SaveAs(Path.Combine”
 
    condition:
        $header at 0 and
        $body and
        filesize < 1KB
}
 
2.
rule webshell_aspx_reGeorgTunnel : Webshell Commodity
{
    meta:
        author = “threatintel@volexity.com”
        date = “2021-03-01”
        description = “A variation on the reGeorg tunnel webshell”
        hash = “406b680edc9a1bb0e2c7c451c56904857848b5f15570401450b73b232ff38928”
        reference = “https://github.com/sensepost/reGeorg/blob/master/tunnel.aspx”
 
    strings:
        $s1 = “System.Net.Sockets”
        $s2 = “System.Text.Encoding.Default.GetString(Convert.FromBase64String(StrTr(Request.Headers.Get”
        // a bit more experimental
        $t1 = “.Split(‘|’)”
        $t2 = “Request.Headers.Get”
        $t3 = “.Substring(“
        $t4 = “new Socket(“
        $t5 = “IPAddress ip;”
 
    condition:
        all of ($s*) or
        all of ($t*)
}
 
3
rule webshell_aspx_sportsball : Webshell Unclassified
{
    meta:
        author = “threatintel@volexity.com”
        date = “2021-03-01”
        description = “The SPORTSBALL webshell allows attackers to upload files or execute commands on the system.”
        hash = “2fa06333188795110bba14a482020699a96f76fb1ceb80cbfa2df9d3008b5b0a”
 
    strings:
        $uniq1 = “HttpCookie newcook = new HttpCookie(\”fqrspt\”, HttpContext.Current.Request.Form”
        $uniq2 = “ZN2aDAB4rXsszEvCLrzgcvQ4oi5J1TuiRULlQbYwldE=”
 
        $var1 = “Result.InnerText = string.Empty;”
        $var2 = “newcook.Expires = DateTime.Now.AddDays(”
        $var3 = “System.Diagnostics.Process process = new System.Diagnostics.Process();”
        $var4 = “process.StandardInput.WriteLine(HttpContext.Current.Request.Form[\””
        $var5 = “else if (!string.IsNullOrEmpty(HttpContext.Current.Request.Form[\””
        $var6 = “<input type=\”submit\” value=\”Upload\” />”
 
    condition:
        any of ($uniq*) or
        all of ($var*)
}

A list of web shell hashes have also been provided by Microsoft:

  • b75f163ca9b9240bf4b37ad92bc7556b40a17e27c2b8ed5c8991385fe07d17d0
  • 097549cf7d0f76f0d99edf8b2d91c60977fd6a96e4b8c3c94b0b1733dc026d3e
  • 2b6f1ebb2208e93ade4a6424555d6a8341fd6d9f60c25e44afe11008f5c1aad1
  • 65149e036fff06026d80ac9ad4d156332822dc93142cf1a122b1841ec8de34b5
  • 511df0e2df9bfa5521b588cc4bb5f8c5a321801b803394ebc493db1ef3c78fa1
  • 4edc7770464a14f54d17f36dc9d0fe854f68b346b27b35a6f5839adf1f13f8ea
  • 811157f9c7003ba8d17b45eb3cf09bef2cecd2701cedb675274949296a6a183d
  • 1631a90eb5395c4e19c7dbcbf611bbe6444ff312eb7937e286e4637cb9e72944

Note: this is not an all-inclusive list of indicators of compromise and threat actors have been known to use short-term leased IP addresses that change very frequently. Organizations that do not locate any of the IOCs in this Alert within your network traffic, may nevertheless have been compromised. CISA recommendations following the guidance located in the Microsoft Advisory to check your servers for any signs of a compromise.  

Conduct Forensic Analysis

Should your organization see evidence of compromise, your incident response should begin with conducting forensic analysis to collect artifacts and perform triage. Please see the following list of recommendations on how to conduct forensic analysis using various tools.

Although the following free tools are not endorsed by the Federal Government, incident responders commonly use them to perform forensics.

While collecting artifacts to perform triage, use processes and tools that minimize the alteration of the data being collected and that minimize impact to the operating system itself.

Ideally, during data collection, store the data on removable/external media and, when possible, run the artifact collection tools from the same media.

Key artifacts for triage that should be collected:

  • Memory
  • All registry hives
  • All windows event logs
  • All web logs

Memory can be collected with a variety of open source tools (e.g., FTK Imager by AccessData, Ram Capture by Belkasoft).

Registry and Windows Event logs can be collected with a variety of open source tools as well (e.g., FTK_Imager, Kroll Artifact Parser And Extractor [KAPE]).

Web logs can also be collected with a variety of open source tools (e.g., FTK Imager).

Windows Artifact Collection Guide

Execute the following steps in order.

1) Download the latest FTK Imager from https://accessdata.com/product-download/.

  • Note: Ensure your review of and compliance with the applicable license associated with the product referenced, which can be found in the product’s User Guide. The United States Government does not endorse any commercial product or service, including any subjects of analysis. Any reference to specific commercial products, processes, or services by service mark, trademark, manufacturer, or otherwise, does not constitute or imply their endorsement, recommendation, or favoring by the United States Government.

2) Collect memory from live system using FTK Imager. See Memory Capture with FTK Imager.pdf for instructions. Note: Download and copy “FTK Imager” folder to an external drive. Run FTK Imager.exe from the FTK Imager folder from external drive. Wait until memory collect is complete before proceeding to step 2.

3) Collect important system artifacts using KAPE. See KAPE Collection Procedure. Note: Download KAPE from a separate system; do not download KAPE to the target system. Run KAPE from external drive.

4) Collect disk image using FTK Imager. See Live Image with FTK Imager.pdf for instructions. Note: Run FTK Imager.exe from the “FTK Imager” folder from external drive.

Memory Capture with FTK Imager

1) Open FTK Imager. Log into the system with Administrator privileges and launch “FTK Imager.”

2) Open “Capture Memory." Select “Capture Memory…” from the File menu.

Figure 1: FTK Imager – Capture Memory Command

3) Select Path and Filenames. On the window that appears, use the “Browse” button to identify the destination of the memory capture. Save the memory capture to an external device and not the main hard drive of the system. Doing so will prevent the saved file from overwriting any dataspace on the system.

  • Name the destination file with a descriptive name (i.e., hostname of the system).
  • Select the box “Include pagefile” and provide a name of the pagefile that is descriptive of the system.
  • Do not select “Create AD1 file.”

Figure 2: FTK Imager – Memory Capture

4) Capture Memory. Click on “Capture Memory” to begin the capture process. The process will take several minutes depending on the size of the pagefile and the amount of memory on the system.

Figure 3: FTK Imager – Capture Process

KAPE Collection Procedure [1]

1) Download KAPE from https://www.kroll.com/en/services/cyber-risk/investigate-and-respond/kroll-artifact-parser-extractor-kape.

2) Disable any antivirus or host protection mechanisms that prevent execution from removable media, or data loss prevention (DLP) mechanisms that restrict utilization of removable media.

  • Enable antivirus and host protection once this process is completed.

3) Unzip Kape.zip and run gkape.exe as admin from your removable media

4) Target source should be the drive on which the OS resides, typically C:.

5) Target destination should be an external drive folder, not the same drive as the Target source. If available, use an external hard drive or flash drive.

  • A KAPE execution with these parameters will typically produce output artifacts with a total size of 1-25 GB.
  • If you are going to be running KAPE on different machines and want to save to the same drive, ensure the Target destination folder is unique for each execution of KAPE.

6) Uncheck Flush checkbox (it is checked natively).

7) Check Add %d and Add %m checkboxes.

8) Select ALL checkboxes to ensure KAPE will target all available data that it is capable of targeting. This takes some time; use the down arrow and space bar to move through the list quickly.

9) Check Process VSCs checkbox.

10) Select Zip radio button and add Base name TargetOutput.

11) Ensure Deduplicate checkbox is checked (it is checked natively).

  • At the bottom you should now see a large Current command line, similar to:
.\kape.exe --tsource C: --tdest E:\%d%m --tflush --target !BasicCollection,!SANS_Triage,Avast,AviraAVLogs,Bitdefender,ComboFix,ESET,FSecure,HitmanPro,Malwarebytes, McAfee,McAfee_ePO,RogueKiller,SentinelOne,Sophos,SUPERAntiSpyware,Symantec_AV_Logs,TrendMicro,VIPRE, Webroot,WindowsDefender,Ammyy,AsperaConnect,BoxDrive,CiscoJabber,CloudStorage,ConfluenceLogs,Discord, Dropbox, Exchange,ExchangeClientAccess,ExchangeTransport,FileZilla,GoogleDrive,iTunesBackup,JavaWebCache,Kaseya,LogMeIn,Notepad++, OneDrive,OutlookPSTOST,ScreenConnect,Skype,TeamViewerLogs,TeraCopy,VNCLogs, Chrome,ChromeExtensions,Edge,Firefox,InternetExplorer,WebBrowsers,ApacheAccessLog,IISLogFiles,ManageEngineLogs, MSSQLErrorLog,NGINXLogs,PowerShellConsole,KapeTriage,MiniTimelineCollection,RemoteAdmin, VirtualDisks, Gigatribe,TorrentClients,Torrents,$Boot,$J,$LogFile,$MFT,$SDS,$T,Amcache,ApplicationEvents,BCD,CombinedLogs, EncapsulationLogging,EventLogs,EventLogs-RDP,EventTraceLogs, EvidenceOfExecution,FileSystem,GroupPolicy,LinuxOnWindowsProfileFiles,LnkFilesAndJumpLists,LogFiles,MemoryFiles, MOF,OfficeAutosave,OfficeDocumentCache,Prefetch,RDPCache,RDPLogs,RecentFileCache,Recycle, RecycleBin, RecycleBinContent,RecycleBinMetadata,RegistryHives,RegistryHivesSystem,RegistryHivesUser,ScheduledTasks,SDB, SignatureCatalog,SRUM,StartupInfo,Syscache,ThumbCache,USBDevicesLogs,WBEM,WER,WindowsFirewall,  WindowsIndexSearch,WindowsNotifcationsDB,WindowsTimeline,XPRestorePoints --vss --zip TargetOutput –gui
  • In the bottom right corner hit the Execute! Button.
  • Screenshot below shows gkape.exe during execution, you will also see a command window execute. Note: KAPE usually takes less than 20 minutes to complete on a workstation; if it is taking significantly longer there may be an issue.

Figure 4: gkape.exe screenshot

Mitigations

CISA strongly recommends organizations read Microsoft’s advisory and security blog post for more information on how to look for this malicious activity and apply critical patches as soon as possible.

If patching is not an immediate option, there are other mitigation options available. However, these options should only be used as a temporary solution, not a replacement for patching.  CISA recommends limiting or blocking external access to internet-facing Exchange Servers via the following:

  • Restrict untrusted connections to port 443, or set up a VPN to separate the Exchange Server from external access; note that this will not prevent an adversary from exploiting the vulnerability if the attacker is already in your network.
  • Block external access to on-premise Exchange:
    • Restrict external access to OWA URL: /owa/. 
    • Restrict external access to Exchange Admin Center (EAC) aka Exchange Control Panel (ECP) URL: /ecp/.

CISA would like to thank Microsoft and Volexity for their contributions to this alert.

RESOURCES

 

References Revisions
  • March 3, 2021: Initial Version

This product is provided subject to this Notification and this Privacy & Use policy.

2021. február 24.

AA21-055A: Exploitation of Accellion File Transfer Appliance

Original release date: February 24, 2021
Summary

This joint advisory is the result of a collaborative effort by the cybersecurity authorities of Australia,[1] New Zealand,[2] Singapore,[3] the United Kingdom,[4] and the United States.[5][6] These authorities are aware of cyber actors exploiting vulnerabilities in Accellion File Transfer Appliance (FTA).[7] This activity has impacted organizations globally, including those in Australia, New Zealand, Singapore, the United Kingdom, and the United States.

Worldwide, actors have exploited the vulnerabilities to attack multiple federal and state, local, tribal, and territorial (SLTT) government organizations as well as private industry organizations including those in the medical, legal, telecommunications, finance, and energy sectors. According to Accellion, this activity involves attackers leveraging four vulnerabilities to target FTA customers.[8] In one incident, an attack on an SLTT organization potentially included the breach of confidential organizational data. In some instances observed, the attacker has subsequently extorted money from victim organizations to prevent public release of information exfiltrated from the Accellion appliance.

This Joint Cybersecurity Advisory provides indicators of compromise (IOCs) and recommended mitigations for this malicious activity. For a downloadable copy of IOCs, see: AA21-055A.stix and MAR-10325064-1.v1.stix.

Click here for a PDF version of this report.

Technical Details

Accellion FTA is a file transfer application that is used to share files. In mid-December 2020, Accellion was made aware of a zero-day vulnerability in Accellion FTA and released a patch on December 23, 2020. Since then, Accellion has identified cyber actors targeting FTA customers by leveraging the following additional vulnerabilities.

  • CVE-2021-27101 – Structured Query Language (SQL) injection via a crafted HOST header (affects FTA 9_12_370 and earlier)
  • CVE-2021-27102 – Operating system command execution via a local web service call (affects FTA versions 9_12_411 and earlier)
  • CVE-2021-27103 – Server-side request forgery via a crafted POST request (affects FTA 9_12_411 and earlier)
  • CVE-2021-27104 – Operating system command execution via a crafted POST request (affects FTA 9_12_370 and earlier)

One of the exploited vulnerabilities (CVE-2021-27101) is an SQL injection vulnerability that allows an unauthenticated user to run remote commands on targeted devices. Actors have exploited this vulnerability to deploy a webshell on compromised systems. The webshell is located on the target system in the file /home/httpd/html/about.html or /home/seos/courier/about.html. The webshell allows the attacker to send commands to targeted devices, exfiltrate data, and clean up logs. The clean-up functionality of the webshell helps evade detection and analysis during post incident response. The Apache /var/opt/cache/rewrite.log file may also contain the following evidence of compromise:

  • [.'))union(select(c_value)from(t_global)where(t_global.c_param)=('w1'))] (1) pass through /courier/document_root.html
  • [.'))union(select(reverse(c_value))from(t_global)where(t_global.c_param)=('w1'))] (1) pass through /courier/document_root.html
  • ['))union(select(loc_id)from(net1.servers)where(proximity)=(0))] (1) pass through /courier/document_root.html

These entries are followed shortly by a pass-through request to sftp_account_edit.php. The entries are the SQL injection attempt indicating an attempt at exploitation of the HTTP header parameter HTTP_HOST.

Apache access logging shows successful file listings and file exfiltration:

  • “GET /courier/about.html?aid=1000 HTTP/1.1” 200 {Response size}
  • “GET /courier/about.htmldwn={Encrypted Path}&fn={encrypted file name} HTTP/1.1” 200 {Response size}

When the clean-up function is run, it modifies archived Apache access logs /var/opt/apache/c1s1-access_log.*.gz and replaces the file contents with the following string:

      Binary file (standard input) matches

In two incidents, the Cybersecurity and Infrastructure Security Agency (CISA) observed a large amount of data transferred over port 443 from federal agency IP addresses to 194.88.104[.]24. In one incident, the Cyber Security Agency of Singapore observed multiple TCP sessions with IP address 45.135.229[.]179.

Organizations are encouraged to investigate the IOCs outlined in this advisory and in [AR21-055A]. If an Accellion FTA appears compromised, organizations can get an indication of the exfiltrated files by obtaining a list of file-last-accessed events for the target files of the symlinks located in the /home/seos/apps/1000/ folder over the period of malicious activity. This information is only indicative and may not be a comprehensive identifier of all exfiltrated files.

Mitigations

Organizations with Accellion FTA should:

  • Temporarily isolate or block internet access to and from systems hosting the software.
  • Assess the system for evidence of malicious activity including the IOCs, and obtain a snapshot or forensic disk image of the system for subsequent investigation.
  • If malicious activity is identified, obtain a snapshot or forensic disk image of the system for subsequent investigation, then:
    • Consider conducting an audit of Accellion FTA user accounts for any unauthorized changes, and consider resetting user passwords.
    • Reset any security tokens on the system, including the “W1” encryption token, which may have been exposed through SQL injection.
  • Update Accellion FTA to version FTA_9_12_432 or later.
  • Evaluate potential solutions for migration to a supported file-sharing platform after completing appropriate testing.
    • Accellion has announced that FTA will reach end-of-life (EOL) on April 30, 2021.[9] Replacing software and firmware/hardware before it reaches EOL significantly reduces risks and costs.

Additional general best practices include:

  • Deploying automated software update tools to ensure that third-party software on all systems is running the most recent security updates provided by the software vendor.
  • Only using up-to-date and trusted third-party components for the software developed by the organization.
  • Adding additional security controls to prevent the access from unauthenticated sources.
Resources References Revisions
  • February 24, 2021: Initial Version

This product is provided subject to this Notification and this Privacy & Use policy.

2021. február 17.

AA21-048A: AppleJeus: Analysis of North Korea’s Cryptocurrency Malware

Original release date: February 17, 2021
Summary

This Advisory uses the MITRE Adversarial Tactics, Techniques, and Common Knowledge (ATT&CK®) framework. See the ATT&CK for Enterprise for all referenced threat actor tactics and techniques.

This joint advisory is the result of analytic efforts among the Federal Bureau of Investigation (FBI), the Cybersecurity and Infrastructure Security Agency (CISA), and the Department of Treasury (Treasury) to highlight the cyber threat to cryptocurrency posed by North Korea, formally known as the Democratic People’s Republic of Korea (DPRK), and provide mitigation recommendations. Working with U.S. government partners, FBI, CISA, and Treasury assess that Lazarus Group—which these agencies attribute to North Korean state-sponsored advanced persistent threat (APT) actors—is targeting individuals and companies, including cryptocurrency exchanges and financial service companies, through the dissemination of cryptocurrency trading applications that have been modified to include malware that facilitates theft of cryptocurrency.

These cyber actors have targeted organizations for cryptocurrency theft in over 30 countries during the past year alone. It is likely that these actors view modified cryptocurrency trading applications as a means to circumvent international sanctions on North Korea—the applications enable them to gain entry into companies that conduct cryptocurrency transactions and steal cryptocurrency from victim accounts. As highlighted in FASTCash 2.0: North Korea's BeagleBoyz Robbing Banks and Guidance on the North Korean Cyber Threat, North Korea’s state-sponsored cyber actors are targeting cryptocurrency exchanges and accounts to steal and launder hundreds of millions of dollars in cryptocurrency.[1][2][3] The U.S. Government refers to malicious cyber activity by the North Korean government as HIDDEN COBRA. For more information on HIDDEN COBRA activity, visit https://www.us-cert.cisa.gov/northkorea.

The U.S. Government has identified malware and indicators of compromise (IOCs) used by the North Korean government to facilitate cryptocurrency thefts; the cybersecurity community refers to this activity as “AppleJeus.” This report catalogues AppleJeus malware in detail. North Korea has used AppleJeus malware posing as cryptocurrency trading platforms since at least 2018. In most instances, the malicious application—seen on both Windows and Mac operating systems—appears to be from a legitimate cryptocurrency trading company, thus fooling individuals into downloading it as a third-party application from a website that seems legitimate. In addition to infecting victims through legitimate-looking websites, HIDDEN COBRA actors also use phishing, social networking, and social engineering techniques to lure users into downloading the malware.

Refer to the following Malware Analysis Reports (MARs) for full technical details of AppleJeus malware and associated IOCs.

Click here for a PDF version of this report.

Technical Details

The North Korean government has used multiple versions of AppleJeus since the malware was initially discovered in 2018. This section outlines seven of the versions below. The MARs listed above provide further technical details of these versions. Initially, HIDDEN COBRA actors used websites that appeared to host legitimate cryptocurrency trading platforms to infect victims with AppleJeus; however, these actors are now also using other initial infection vectors, such as phishing, social networking, and social engineering techniques, to get users to download the malware.

Targeted Nations

HIDDEN COBRA actors have targeted institutions with AppleJeus malware in several sectors, including energy, finance, government, industry, technology, and telecommunications. Since January 2020, the threat actors have targeted these sectors in the following countries: Argentina, Australia, Belgium, Brazil, Canada, China, Denmark, Estonia, Germany, Hong Kong, Hungary, India, Ireland, Israel, Italy, Japan, Luxembourg, Malta, the Netherlands, New Zealand, Poland, Russia, Saudi Arabia, Singapore, Slovenia, South Korea, Spain, Sweden, Turkey, the United Kingdom, Ukraine, and the United States (figure 1).

 


 
Figure 1: Countries targeted with AppleJeus by HIDDEN COBRA threat actors since 2020

AppleJeus Versions Note

The version numbers used for headings in this document correspond to the order the AppleJeus campaigns were identified in open source or through other investigative means. These versions may or may not be in the correct order to develop or deploy the AppleJeus campaigns.

AppleJeus Version 1: Celas Trade Pro Introduction and Infrastructure

In August 2018, open-source reporting disclosed information about a trojanized version of a legitimate cryptocurrency trading application on an undisclosed victim’s computer. The malicious program, known as Celas Trade Pro, was a modified version of the benign Q.T. Bitcoin Trader application. This incident led to the victim company being infected with a Remote Administration Tool (RAT) known as FALLCHILL, which was attributed to North Korea (HIDDEN COBRA) by the U.S. Government. FALLCHILL is a fully functional RAT with multiple commands that the adversary can issue from a command and control (C2) server to infected systems via various proxies. FALLCHILL typically infects a system as a file dropped by other HIDDEN COBRA malware (Develop Capabilities: Malware [T1587.001]). Because of this, additional HIDDEN COBRA malware may be present on systems compromised with FALLCHILL.[4]

Further research revealed that a phishing email from a Celas LLC company (Phishing: Spearphishing Link [T1566.002]) recommended the trojanized cryptocurrency trading application to victims. The email provided a link to the Celas’ website, celasllc[.]com (Acquire Infrastructure: Domain [T1583.001]), where the victim could download a Windows or macOS version of the trojanized application.

The celasllc[.]com domain resolved to the following Internet Protocol (IP) addresses from May 29, 2018, to January 23, 2021.

  • 45.199.63[.]220
  • 107.187.66[.]103
  • 145.249.106[.]19
  • 175.29.32[.]160
  • 185.142.236[.]213
  • 185.181.104[.]82
  • 198.251.83[.]27
  • 208.91.197[.]46
  • 209.99.64[.]18

The celasllc[.]com domain had a valid Sectigo (previously known as Comodo) Secure Sockets Layer (SSL) certificate (Obtain Capabilities: Digital Certificates [T1588.004]). The SSL certificate was “Domain Control Validated,” a weak security verification level that does not require validation of the owner’s identity or the actual business’s existence.

Celas Trade Pro Application Analysis Windows Program

The Windows version of the malicious Celas Trade Pro application is an MSI Installer (.msi). The MSI Installer installation package comprises a software component and an application programming interface (API) that Microsoft uses for the installation, maintenance, and removal of software. The installer looks legitimate and is signed by a valid Sectigo certificate that was purchased by the same user as the SSL certificate for celasllc[.]com (Obtain Capabilities: Code Signing Certificates [T1588.003]). The MSI Installer asks the victim for administrative privileges to run (User Execution: Malicious File [T1204.002]).

Once permission is granted, the threat actor is able to run the program with elevated privileges (Abuse Elevation Control Mechanism [T1548]) and MSI executes the following actions.

  • Installs CelasTradePro.exe in folder C:\Program Files (x86)\CelasTradePro
  • Installs Updater.exe in folder C:\Program Files (x86)\CelasTradePro
  • Runs Updater.exe with the CheckUpdate parameters

The CelasTradePro.exe program asks for the user’s exchange and loads a legitimate-looking cryptocurrency trading platform—very similar to the benign Q.T. Bitcoin Trader—that exhibits no signs of malicious activity.

The Updater.exe program has the same program icon as CelasTradePro.exe. When run, it checks for the CheckUpdate parameter, collects the victim’s host information (System Owner/User Discovery [T1033]), encrypts the collected information with a hardcoded XOR encryption, and sends information to a C2 website (Exfiltration Over C2 Channel [T1041]).

macOS X Program

The macOS version of the malicious application is a DMG Installer that has a disk image format that Apple commonly uses to distribute software over the internet. The installer looks legitimate and has a valid digital signature from Sectigo (Obtain Capabilities: Digital Certificates [T1588.004]). It has very similar functionality to the Windows version. The installer executes the following actions.

  • Installs CelasTradePro in folder /Applications/CelasTradePro.app/Contents/MacOS/
  • Installs Updater in folder /Applications/CelasTradePro.app/Contents/MacOS
  • Executes a postinstall script
    • Moves .com.celastradepro.plist to folder LaunchDaemons
    • Runs Updater with the CheckUpdate parameter

CelasTradePro asks for the user’s exchange and loads a legitimate-looking cryptocurrency trading platform—very similar to the benign Q.T. Bitcoin Trader—that exhibits no signs of malicious activity.

Updater checks for the CheckUpdate parameter and, when found, it collects the victim’s host information (System Owner/User Discovery [T1033]), encrypts the collected information with a hardcoded XOR key before exfiltration, and sends the encrypted information to a C2 website (Exfiltration Over C2 Channel [T1041]). This process helps the adversary obtain persistence on a victim’s network.

The postinstall script is a sequence of instructions that runs after successfully installing an application (Command and Scripting Interpreter: AppleScript [T1059.002]). This script moves property list (plist) file .com.celastradepro.plist from the installer package to the LaunchDaemons folder (Scheduled Task/Job: Launchd [T1053.004]). The leading “.” makes it unlisted in the Finder app or default Terminal directory listing (Hide Artifacts: Hidden Files and Directories [T1564.001]). Once in the folder, this property list (plist) file will launch the Updater program with the CheckUpdate parameter on system load as Root for every user. Because the LaunchDaemon will not run automatically after the plist file is moved, the postinstall script launches the Updater program with the CheckUpdate parameter and runs it in the background (Create or Modify System Process: Launch Daemon [T1543.004]).

Payload

After a cybersecurity company published a report detailing the above programs and their malicious extras, the website was no longer accessible. Since this site was the C2 server, the payload cannot be confirmed. The cybersecurity company that published the report states the payload was an encrypted and obfuscated binary (Obfuscated Files or Information [T1027]), which eventually drops FALLCHILL onto the machine and installs it as a service (Create or Modify System Process: Windows Service [T1543.003]). FALLCHILL malware uses an RC4 encryption algorithm with a 16-byte key to protect its communications (Encrypted Channel: Symmetric Cryptography [T1573.001]). The key employed in these versions has also been used in a previous version of FALLCHILL.[5][6]

For more details on AppleJeus Version 1: Celas Trade Pro, see MAR-10322463-1.v1.

AppleJeus Version 2: JMT Trading Introduction and Infrastructure

In October 2019, a cybersecurity company identified a new version of the AppleJeus malware—JMT Trading—thanks to its many similarities to the original AppleJeus malware. Again, the malware was in the form of a cryptocurrency trading application, which a legitimate-looking company, called JMT Trading, marketed and distributed on their website, jmttrading[.]org (Acquire Infrastructure: Domain [T1583.001]). This website contained a “Download from GitHub” button, which linked to JMT Trading’s GitHub page (Acquire Infrastructure: Web Services [T1583.006]), where Windows and macOS X versions of the JMT Trader application were available for download (Develop Capabilities: Malware [T1587.001]). The GitHub page also included .zip and tar.gz files containing the source code.

The jmttrading[.]org domain resolved to the following IP addresses from October 15, 2016, to January 22, 2021.

  • 45.33.2[.]79
  • 45.33.23[.]183
  • 45.56.79[.]23
  • 45.79.19[.]196
  • 96.126.123[.]244
  • 146.112.61[.]107
  • 184.168.221[.]40
  • 184.168.221[.]57
  • 198.187.29[.]20
  • 198.54.117[.]197
  • 198.54.117[.]198
  • 198.54.117[.]199
  • 198.54.117[.]200
  • 198.58.118[.]167

The jmttrading[.]org domain had a valid Sectigo SSL certificate (Obtain Capabilities: Digital Certificates [T1588.004]). The SSL certificate was “Domain Control Validated,” a weak security verification level that does not require validation of the owner’s identity or the actual business’s existence. The current SSL certificate was issued by Let’s Encrypt.

JMT Trading Application Analysis Windows Program

The Windows version of the malicious cryptocurrency application is an MSI Installer. The installer looks legitimate and has a valid digital signature from Sectigo (Obtain Capabilities: Digital Certificates [T1588.004]). The signature was signed with a code signing certificate purchased by the same user as the SSL certificate for jmttrading[.]org (Obtain Capabilities: Code Signing Certificates [T1588.003]). The MSI Installer asks the victim for administrative privileges to run (User Execution: Malicious File [T1204.002]).

Once permission is granted, the MSI executes the following actions.

  • Installs JMTTrader.exe in folder C:\Program Files (x86)\JMTTrader
  • Installs CrashReporter.exe in folder C:\Users\<username>\AppData\Roaming\JMTTrader
  • Runs CrashReporter.exe with the Maintain parameter

The JMTTrader.exe program asks for the user’s exchange and loads a legitimate-looking cryptocurrency trading platform—very similar to CelasTradePro.exe and the benign Q.T. Bitcoin Trader—that exhibits no signs of malicious activity.

The program CrashReporter.exe is heavily obfuscated with the ADVObfuscation library, renamed “snowman” (Obfuscated Files or Information [T1027]). When run, it checks for the Maintain parameter and collects the victim’s host information (System Owner/User Discovery [T1033]), encrypts the collected information with a hardcoded XOR key before exfiltration, and sends the encrypted information to a C2 website (Exfiltration Over C2 Channel [T1041]). The program also creates a scheduled SYSTEM task, named JMTCrashReporter, which runs CrashReporter.exe with the Maintain parameter at any user’s login (Scheduled Task/Job: Scheduled Task [T1053.005]).

macOS X Program

The macOS version of the malicious application is a DMG Installer. The installer looks legitimate and has very similar functionality to the Windows version, but it does not have a digital certificate and will warn the user of that before installation. The installer executes the following actions.

  • Installs JMTTrader in folder /Applications/JMTTrader.app/Contents/MacOS/
  • Installs .CrashReporter in folder /Applications/JMTTrader.app/Contents/Resources/
    • Note: the leading “.” makes it unlisted in the Finder app or default Terminal directory listing.
  • Executes a postinstall script
    • Moves .com.jmttrading.plist to folder LaunchDaemons
    • Changes the file permissions on the plist
    • Runs CrashReporter with the Maintain parameter
    • Moves .CrashReporter to folder /Library/JMTTrader/CrashReporter
    • Makes .CrashReporter executable

The JMTTrader program asks for the user’s exchange and loads a legitimate-looking cryptocurrency trading platform—very similar to CelasTradePro and the benign Q.T. Bitcoin Trader—that exhibits no signs of malicious activity.

The CrashReporter program checks for the Maintain parameter and is not obfuscated. This lack of obfuscation makes it easier to determine the program’s functionality in detail. When it finds the Maintain parameter, it collects the victim’s host information (System Owner/User Discovery [T1033]), encrypts the collected information with a hardcoded XOR key before exfiltration, and sends the encrypted information to a C2 website (Exfiltration Over C2 Channel [T1041]).

The postinstall script has similar functionality to the one used by CelasTradePro, but it has a few additional features (Command and Scripting Interpreter: AppleScript [T1059.002]). It moves the property list (plist) file .com.jmttrading.plist from the Installer package to the LaunchDaemons folder (Scheduled Task/Job: Launchd [T1053.004]), but also changes the file permissions on the plist file. Once in the folder, this property list (plist) file will launch the CrashReporter program with the Maintain parameter on system load as Root for every user. Also, the postinstall script moves the .CrashReporter program to a new location /Library/JMTTrader/CrashReporter and makes it executable. Because the LaunchDaemon will not run automatically after the plist file is moved, the postinstall script launches CrashReporter with the Maintain parameter and runs it in the background (Create or Modify System Process: Launch Daemon [T1543.004]).

Payload

Soon after the cybersecurity company tweeted about JMT Trader on October 11, 2019, the files on GitHub were updated to clean, non-malicious installers. Then on October 13, 2019, a different cybersecurity company published an article detailing the macOS X JMT Trader, and soon after, the C2 beastgoc[.]com website went offline. There is not a confirmed sample of the payload to analyze at this point.

For more details on AppleJeus Version 2: JMT Trading, see MAR-10322463-2.v1.

AppleJeus Version 3: Union Crypto Introduction and Infrastructure

In December 2019, another version of the AppleJeus malware was identified on Twitter by a cybersecurity company based on many similarities to the original AppleJeus malware. Again, the malware was in the form of a cryptocurrency trading application, which was marketed and distributed by a legitimate-looking company, called Union Crypto, on their website, unioncrypto[.]vip (Acquire Infrastructure: Domain [T1583.001]). Although this website is no longer available, a cybersecurity researcher discovered a download link, https://www.unioncrypto[.]vip/download/W6c2dq8By7luMhCmya2v97YeN, recorded on VirusTotal for the macOS X version of UnionCryptoTrader. In contrast, open-source reporting stated that the Windows version might have been downloaded via instant messaging service Telegram, as it was found in a “Telegram Downloads” folder on an unnamed victim.[7]

The unioncrypto[.]vip domain resolved to the following IP addresses from June 5, 2019, to July 15, 2020.

  • 104.168.167[.]16
  • 198.54.117[.]197
  • 198.54.117[.]198
  • 198.54.117[.]199
  • 198.54.117[.]200

The domain unioncrypto[.]vip had a valid Sectigo SSL certificate (Obtain Capabilities: Digital Certificates [T1588.004]). The SSL certificate was “Domain Control Validated,” a weak security verification level that does not require validation of the owner’s identity or the actual business’s existence.

Union Crypto Trader Application Analysis Windows Program

The Windows version of the malicious cryptocurrency application is a Windows executable (.exe) (User Execution: Malicious File [T1204.002]), which acts as an installer that extracts a temporary MSI Installer.

The Windows program executes the following actions.

  • Extracts UnionCryptoTrader.msi to folder C:\Users\<username>\AppData\Local\Temp\{82E4B719-90F74BD1-9CF1-56CD777E0C42}
  • Runs UnionCryptoUpdater.msi
    • Installs UnionCryptoTrader.exe in folder C:\Program Files\UnionCryptoTrader
    • Installs UnionCryptoUpdater.exe in folder C:\Users\<username>\AppData\Local\UnionCryptoTrader
  • Deletes UnionCryptoUpdater.msi
  • Runs UnionCryptoUpdater.exe

The program UnionCryptoTrader.exe loads a legitimate-looking cryptocurrency arbitrage application—defined as “the simultaneous buying and selling of securities, currency, or commodities in different markets or in derivative forms to take advantage of differing prices for the same asset”—which exhibits no signs of malicious activity. This application is very similar to another cryptocurrency arbitrage application known as Blackbird Bitcoin Arbitrage.[8]

The program UnionCryptoUpdater.exe first installs itself as a service (Create or Modify System Process: Windows Service [T1543.003]), which will automatically start when any user logs on (Boot or Logon Autostart Execution [T1547]). The service is installed with a description stating it “Automatically installs updates for Union Crypto Trader.” When launched, it collects the victim’s host information (System Owner/User Discovery [T1033]), combines the information in a string that is MD5 hashed and stored in the auth_signature variable before exfiltration, and sends it to a C2 website (Exfiltration Over C2 Channel [T1041]).

macOS X Program

The macOS version of the malicious application is a DMG Installer. The installer looks legitimate and has very similar functionality to the Windows version, but it does not have a digital certificate and will warn the user of that before installation. The installer executes the following actions.

  • Installs UnionCryptoTrader in folder /Applications/UnionCryptoTrader.app/Contents/MacOS/
  • Installs .unioncryptoupdater in folder /Applications/UnionCryptoTrader.app/Contents/Resources/
    • Note: the leading “.” makes it unlisted in the Finder app or default Terminal directory listing
  • Executes a postinstall script
    • Moves .vip.unioncrypto.plist to folder LaunchDaemons
    • Changes the file permissions on the plist to Root
    • Runs unioncryptoupdater
    • Moves .unioncryptoupdater to folder /Library/UnionCrypto/unioncryptoupdater
    • Makes .unioncryptoupdater executable

The UnionCryptoTrader program loads a legitimate-looking cryptocurrency arbitrage application, which exhibits no signs of malicious activity. The application is very similar to another cryptocurrency arbitrage application known as Blackbird Bitcoin Arbitrage.

The .unioncryptoupdater program is signed ad-hoc, meaning it is not signed with a valid code-signing identity. When launched, it collects the victim’s host information (System Owner/User Discovery [T1033]), combines the information in a string that is MD5 hashed and stored in the auth_signature variable before exfiltration, and sends it to a C2 website (Exfiltration Over C2 Channel [T1041]).

The postinstall script has similar functionality to the one used by JMT Trading (Command and Scripting Interpreter: AppleScript [T1059.002]). It moves the property list (plist) file .vip.unioncrypto.plist from the Installer package to the LaunchDaemons folder (Scheduled Task/Job: Launchd [T1053.004]), but also changes the file permissions on the plist file to Root. Once in the folder, this property list (plist) file will launch the .unioncryptoupdater on system load as Root for every user. The postinstall script moves the .unioncryptoupdater program to a new location /Library/UnionCrypto/unioncryptoupdater and makes it executable. Because the LaunchDaemon will not run automatically after the plist file is moved, the postinstall script launches .unioncryptoupdater and runs it in the background (Create or Modify System Process: Launch Daemon [T1543.004]).

Payload

The payload for the Windows malware is a Windows Dynamic-Link-Library. UnionCryptoUpdater.exe does not immediately download the stage 2 malware but instead downloads it after a time specified by the C2 server. This delay could be implemented to prevent researchers from directly obtaining the stage 2 malware.

The macOS X malware’s payload could not be downloaded, as the C2 server is no longer accessible. Additionally, none of the open-source reporting for this sample contained copies of the macOS X payload. The macOS X payload is likely similar in functionality to the Windows stage 2 detailed above.

For more details on AppleJeus Version 3: Union Crypto, see MAR-10322463-3.v1.

Commonalities between Celas Trade Pro, JMT Trading, and Union Crypto Hardcoded Values

In each AppleJeus version, there are hardcoded values used for encryption or to create a signature when combined with the time (table 1).

Table 1: AppleJeus hardcoded values and uses

AppleJeus Version Value Use 1: Celas Trade Pro Moz&Wie;#t/6T!2y XOR encryption to send data 1: Celas Trade Pro W29ab@ad%Df324V$Yd RC4 decryption 2: JMT Trader Windows X,%`PMk--Jj8s+6=15:20:11 XOR encryption to send data 2: JMT Trader OSX X,%`PMk--Jj8s+6=\x02 XOR encryption to send data 3: Union Crypto Trader 12GWAPCT1F0I1S14 Combined with time for signature

 

The Union Crypto Trader and Celas LLC (XOR) values are 16 bytes in length. For JMT Trader, the first 16 bytes of the Windows and macOS X values are identical, and the additional bytes are in a time format for the Windows sample. The structure of a 16-byte value combined with the time is also used in Union Crypto Trader to create the auth_signature.

As mentioned, FALLCHILL was reported as the final payload for Celas Trade Pro. All FALLCHILL samples use 16-byte hardcoded RC4 keys for sending data, similar to the 16-byte keys in the AppleJeus samples.

Open-Source Cryptocurrency Applications

All three AppleJeus samples are bundled with modified copies of legitimate cryptocurrency applications and can be used as originally designed to trade cryptocurrency. Both Celas LLC and JMT Trader modified the same cryptocurrency application, Q.T. Bitcoin Trader; Union Crypto Trader modified the Blackbird Bitcoin Arbitrage application.

Postinstall Scripts, Property List Files, and LaunchDaemons

The macOS X samples of all three AppleJeus versions contain postinstall scripts with similar logic. The Celas LLC postinstall script only moves the plist file to a new location and launches Updater with the CheckUpdate parameter in the background. The JMT Trader and Union Crypto Trader also perform these actions and have identical functionality. The additional actions performed by both postinstall scripts are to change the file permissions on the plist, make a new directory in the /Library folder, move CrashReporter or UnionCryptoUpdater to the newly created folder, and make them executable.

The plist files for all three AppleJeus files have identical functionality. They only differ in the files’ names and one default comment that was not removed from the Celas LLC plist. As the logic and functionality of the postinstall scripts and plist files are almost identical, the LaunchDaemons created also function the same.

They will all launch the secondary executable as Root on system load for every user.

AppleJeus Version 4: Kupay Wallet Introduction and Infrastructure

On March 13, 2020, a new version of the AppleJeus malware was identified. The malware was marketed and distributed by a legitimate-looking company, called Kupay Wallet, on their website kupaywallet[.]com (Acquire Infrastructure: Domain [T1583.001]).

The domain www.kupaywallet[.]com resolved to IP address 104.200.67[.]96 from March 20, 2020, to January 16, 2021. CrownCloud US, LLC controlled the IP address (autonomous system number [ASN] 8100), and is located in New York, NY.

The domain www.kupaywallet[.]com had a valid Sectigo SSL certificate (Obtain Capabilities: Digital Certificates [T1588.004]). The SSL certificate was “Domain Control Validated,” a weak security verification level that does not require validation of the owner’s identity or the actual business’s existence.

Kupay Wallet Application Analysis Windows Program

The Windows version of the malicious cryptocurrency application is an MSI Installer. The MSI executes the following actions.

  • Installs Kupay.exe in folder C:\Program Files (x86)\Kupay
  • Installs KupayUpgrade.exe in folder C:\Users\<username>\AppData\Roaming\KupaySupport
  • Runs KupayUpgrade.exe

The program Kupay.exe loads a legitimate-looking cryptocurrency wallet platform, which exhibits no signs of malicious activity and is very similar to an open-source platform known as Copay, distributed by Atlanta-based company BitPay.

The program KupayUpgrade.exe first installs itself as a service (Create or Modify System Process: Windows Service [T1543.003]), which will automatically start when any user logs on (Boot or Logon Autostart Execution [T1547]). The service is installed with a description stating it is an “Automatic Kupay Upgrade.” When launched, it collects the victim’s host information (System Owner/User Discovery [T1033]), combines the information in strings before exfiltration, and sends it to a C2 website (Exfiltration Over C2 Channel [T1041]).

macOS X Program

The macOS version of the malicious application is a DMG Installer. The installer looks legitimate and has very similar functionality to the Windows version, but it does not have a digital certificate and will warn the user of that before installation. The installer executes the following actions.

  • Installs Kupay in folder /Applications/Kupay.app/Contents/MacOS/
  • Installs kupay_upgrade in folder /Applications/Kupay.app/Contents/MacOS/
  • Executes a postinstall script
    • Creates KupayDaemon folder in /Library/Application Support folder
    • Moves kupay_upgrade to the new folder
    • Moves com.kupay.pkg.wallet.plist to folder /Library/LaunchDaemons/
    • Runs the command launchctl load to load the plist without a restart
    • Runs kupay_upgrade in the background

Kupay is likely a copy of an open-source cryptocurrency wallet application, loads a legitimate-looking wallet program (fully functional), and its functionality is identical to the Windows Kupay.exe program.

The kupay_upgrade program calls its function CheckUpdate (which contains most of the logic functionality of the malware) and sends a POST to the C2 server with a connection named “Kupay Wallet 9.0.1 (Check Update Osx)” (Application Layer Protocol: Web Protocols [T1071.001]). If the C2 server returns a file, it is decoded and written to the victim’s folder /private/tmp/kupay_update with permissions set by the command chmod 700 (only the user can read, write, and execute) (Command and Scripting Interpreter [T1059]). Stage 2 is then launched, and the malware, kupay_upgrade, returns to sleeping and checking in with the C2 server at predetermined intervals (Application Layer Protocol: Web Protocols [T1071.001]).

The postinstall script has similar functionality to other AppleJeus scripts (Command and Scripting Interpreter: AppleScript [T1059.002]). It creates the KupayDaemon folder in /Library/Application Support folder and then moves kupay_upgrade to the new folder. It moves the property list (plist) file com.kupay.pkg.wallet.plist from the Installer package to the /Library/LaunchDaemons/ folder (Scheduled Task/Job: Launchd [T1053.004]). The script runs the command launchctl load to load the plist without a restart (Command and Scripting Interpreter [T1059]). But, since the LaunchDaemon will not run automatically after the plist file is moved, the postinstall script launches kupay_upgrade and runs it in the background (Create or Modify System Process: Launch Daemon [T1543.004]).

Payload

The Windows malware’s payload could not be downloaded since the C2 server is no longer accessible. Additionally, none of the open-source reporting for this sample contained copies of the payload. The Windows payload is likely similar in functionality to the macOS X stage 2 detailed below.

The stage 2 payload for the macOS X malware was decoded and analyzed. The stage 2 malware has a variety of functionalities. Most importantly, it checks in with a C2 and, after connecting to the C2, can send or receive a payload, read and write files, execute commands via the terminal, etc.

For more details on AppleJeus Version 4: Kupay Wallet, see MAR-10322463-4.v1.

AppleJeus Version 5: CoinGoTrade Introduction and Infrastructure

In early 2020, another version of the AppleJeus malware was identified. This time the malware was marketed and distributed by a legitimate-looking company called CoinGoTrade on their website coingotrade[.]com (Acquire Infrastructure: Domain [T1583.001]).

The domain CoinGoTrade[.]com resolved to IP address 198.54.114[.]175 from February 28, 2020, to January 23, 2021. The IP address is controlled by NameCheap Inc. (ASN 22612) and is located in Atlanta, GA. This IP address is in the same ASN for Dorusio[.]com and Ants2Whale[.]com.

The domain CoinGoTrade[.]com had a valid Sectigo SSL certificate (Obtain Capabilities: Digital Certificates [T1588.004]). The SSL certificate was “Domain Control Validated,” a weak security verification level that does not require validation of the owner’s identity or the actual business’s existence.

CoinGoTrade Application Analysis Windows Program

The Windows version of the malicious application is an MSI Installer. The installer appears to be legitimate and will execute the following actions.

  • Installs CoinGoTrade.exe in folder C:\Program Files (x86)\CoinGoTrade
  • Installs CoinGoTradeUpdate.exe in folder C:\Users\<username>\AppData\Roaming\CoinGoTradeSupport
  • Runs CoinGoTradeUpdate.exe

CoinGoTrade.exe loads a legitimate-looking cryptocurrency wallet platform with no signs of malicious activity and is a copy of an open-source cryptocurrency application.

CoinGoTradeUpdate.exe first installs itself as a service (Create or Modify System Process: Windows Service [T1543.003]), which will automatically start when any user logs on (Boot or Logon Autostart Execution [T1547]). The service is installed with a description stating it is an “Automatic CoinGoTrade Upgrade.” When launched, it collects the victim’s host information (System Owner/User Discovery [T1033]), combines the information in strings before exfiltration, and sends it to a C2 website (Exfiltration Over C2 Channel [T1041]).

macOS X Program

The macOS version of the malicious application is a DMG Installer. The installer looks legitimate and has very similar functionality to the Windows version, but it does not have a digital certificate and will warn the user of that before installation. The installer executes the following actions.

  • Installs CoinGoTrade in folder /Applications/CoinGoTrade.app/Contents/MacOS/
  • Installs CoinGoTradeUpgradeDaemon in folder /Applications/CoinGoTrade.app/Contents/MacOS/
  • Executes a postinstall script
    • Creates CoinGoTradeService folder in /Library/Application Support folder
    • Moves CoinGoTradeUpgradeDaemon to the new folder
    • Moves com.coingotrade.pkg.product.plist to folder /Library/LaunchDaemons/
    • Runs CoinGoTradeUpgradeDaemon in the background

The CoinGoTrade program is likely a copy of an open-source cryptocurrency wallet application and loads a legitimate-looking, fully functional wallet program).

The CoinGoTradeUpgradeDaemon program calls its function CheckUpdate (which contains most of the logic functionality of the malware) and sends a POST to the C2 server with a connection named “CoinGoTrade 1.0 (Check Update Osx)” (Application Layer Protocol: Web Protocols [T1071.001]). If the C2 server returns a file, it is decoded and written to the victim’s folder /private/tmp/updatecoingotrade with permissions set by the command chmod 700 (only the user can read, write, and execute) (Command and Scripting Interpreter [T1059]). Stage 2 is then launched, and the malware, CoinGoTradeUpgradeDaemon, returns to sleeping and checking in with the C2 server at predetermined intervals (Application Layer Protocol: Web Protocols [T1071.001]).

The postinstall script has similar functionality to the other scripts (Command and Scripting Interpreter: AppleScript [T1059.002]) and installs CoinGoTrade and CoinGoTradeUpgradeDaemon in folder /Applications/CoinGoTrade.app/Contents/MacOS/. It moves the property list (plist) file com.coingotrade.pkg.product.plist to the /Library/LaunchDaemons/ folder (Scheduled Task/Job: Launchd [T1053.004]). Because the LaunchDaemon will not run automatically after the plist file is moved, the postinstall script launches CoinGoTradeUpgradeDaemon and runs it in the background (Create or Modify System Process: Launch Daemon [T1543.004]).

Payload

The Windows malware’s payload could not be downloaded because the C2 server is no longer accessible. Additionally, none of the open-source reporting for this sample contained copies of the payload. The Windows payload is likely similar in functionality to the macOS X stage 2 detailed below.

The stage 2 payload for the macOS X malware was no longer available from the specified download URL. Still, a file was submitted to VirusTotal by the same user on the same date as the macOS X CoinGoTradeUpgradeDaemon. These clues suggest that the submitted file may be related to the macOS X version of the malware and the downloaded payload.

The file prtspool is a 64-bit Mach-O executable with a large variety of features that have all been confirmed as functionality. The file has three C2 URLs hardcoded into the file and communicates to these with HTTP POST multipart-form data boundary string. Like other HIDDEN COBRA malware, prtspool uses format strings to store data collected about the system and sends it to the C2s.

For more details on AppleJeus Version 5: CoinGoTrade, see MAR-10322463-5.v1.

AppleJeus Version 6: Dorusio Introduction and Infrastructure

In March 2020, an additional version of the AppleJeus malware was identified. This time the malware was marketed and distributed by a legitimate-looking company called Dorusio on their website, dorusio[.]com (Acquire Infrastructure: Domain [T1583.001]). Researchers collected samples for Windows and macOS X versions of the Dorusio Wallet (Develop Capabilities: Malware [T1587.001]). As of at least early 2020, the actual download links result in 404 errors. The download page has release notes with version revisions claiming to start with version 1.0.0, released on April 15, 2019.

The domain dorusio[.]com resolved to IP address 198.54.115[.]51 from March 30, 2020 to January 23, 2021. The IP address is controlled by NameCheap Inc. (ASN 22612) and is located in Atlanta, GA. This IP address is in the same ASN for CoinGoTrade[.]com and Ants2Whale[.]com.

The domain dorusio[.]com had a valid Sectigo SSL certificate (Obtain Capabilities: Digital Certificates [T1588.004]). The SSL certificate was “Domain Control Validated,” a weak security verification level that does not require validation of the owner’s identity or the actual business’s existence.

Dorusio Application Analysis Windows Program

The Windows version of the malicious application is an MSI Installer. The installer appears to be legitimate and will install the following two programs.

  • Installs Dorusio.exe in folder C:\Program Files (x86)\Dorusio
  • Installs DorusioUpgrade.exe in folder C:\Users\<username>\AppData\Roaming\DorusioSupport
  • Runs DorusioUpgrade.exe

The program, Dorusio.exe, loads a legitimate-looking cryptocurrency wallet platform with no signs of malicious activity and is a copy of an open-source cryptocurrency application.

The program DorusioUpgrade.exe first installs itself as a service (Create or Modify System Process: Windows Service [T1543.003]), which will automatically start when any user logs on (Boot or Logon Autostart Execution [T1547]). The service is installed with a description stating it “Automatic Dorusio Upgrade.” When launched, it collects the victim’s host information (System Owner/User Discovery [T1033]), combines the information in strings before exfiltration, and sends it to a C2 website (Exfiltration Over C2 Channel [T1041]).

macOS X Program

The macOS version of the malicious application is a DMG Installer. The installer looks legitimate and has very similar functionality to the Windows version, but it does not have a digital certificate and will warn the user of that before installation. The installer executes the following actions.

  • Installs Dorusio in folder /Applications/Dorusio.app/Contents/MacOS/
  • Installs Dorusio_upgrade in folder /Applications/Dorusio.app/Contents/MacOS/
  • Executes a postinstall script
    • Creates DorusioDaemon folder in /Library/Application Support folder
    • Moves Dorusio_upgrade to the new folder
    • Moves com.dorusio.pkg.wallet.plist to folder /Library/LaunchDaemons/
    • Runs Dorusio_upgrade in the background

The Dorusio program is likely a copy of an open-source cryptocurrency wallet application and loads a legitimate-looking wallet program (fully functional). Aside from the Dorusio logo and two new services, the wallet appears to be the same as the Kupay Wallet. This application seems to be a modification of the open-source cryptocurrency wallet Copay distributed by Atlanta-based company BitPay.

The Dorusio_upgrade program calls its function CheckUpdate (which contains most of the logic functionality of the malware) and sends a POST to the C2 server with a connection named “Dorusio Wallet 2.1.0 (Check Update Osx)” (Application Layer Protocol: Web Protocols [T1071.001]). If the C2 server returns a file, it is decoded and written to the victim’s folder /private/tmp/Dorusio_update with permissions set by the command chmod 700 (only the user can read, write, and execute) (Command and Scripting Interpreter [T1059]). Stage 2 is then launched, and the malware, Dorusio_upgrade, returns to sleeping and checking in with the C2 server at predetermined intervals (Application Layer Protocol: Web Protocols [T1071.001]).

The postinstall script has similar functionality to other AppleJeus scripts (Command and Scripting Interpreter: AppleScript [T1059.002]). It creates the DorusioDaemon folder in /Library/Application Support folder and then moves Dorusio_upgrade to the new folder. It moves the property list (plist) file com.dorusio.pkg.wallet.plist from the Installer package to the /Library/LaunchDaemons/ folder (Scheduled Task/Job: Launchd [T1053.004]). Because the LaunchDaemon will not run automatically after the plist file is moved, the postinstall script launches Dorusio_upgrade and runs it in the background (Create or Modify System Process: Launch Daemon [T1543.004]).

Payload

Neither the payload for the Windows nor macOS X malware could be downloaded; the C2 server is no longer accessible. The payloads are likely similar in functionality to the macOS X stage 2 from CoinGoTrade and Kupay Wallet, or the Windows stage 2 from Union Crypto.

For more details on AppleJeus Version 6: Dorusio, see MAR-10322463-6.v1.

AppleJeus 4, 5, and 6 Installation Conflictions

If a user attempts to install the Kupay Wallet, CoinGoTrade, and Dorusio applications on the same system, they will encounter installation conflicts.

If Kupay Wallet is already installed on a system and the user tries to install CoinGoTrade or Dorusio:

  • Pop-up windows appear, stating a more recent version of the program is already installed.

If CoinGoTrade is already installed on a system and the user attempts to install Kupay Wallet:

  • Kupay.exe will be installed in the C:\Program Files (x86)\CoinGoTrade\ folder.
  • All CoinGoTrade files will be deleted.
  • The folders and files contained in the C:\Users\<username>\AppData\Roaming\CoinGoTradeSupport will remain installed.
  • KupayUpgrade.exe is installed in the new folder C:\Users\<username>\AppData\Roaming\KupaySupport.

If Dorusio is already installed on a system and the user attempts to install Kupay Wallet:

  • Kupay.exe will be installed in the C:\Program Files (x86)\Dorusio\ folder.
  • All Dorusio.exe files will be deleted.
  • The folders and files contained in C:\Users\<username>\AppData\Roaming\DorusioSupport will remain installed.
  • KupayUpgrade.exe is installed in the new folder C:\Users\<username>\AppData\Roaming\KupaySupport.
AppleJeus Version 7: Ants2Whale Introduction and Infrastructure

In late 2020, a new version of AppleJeus was identified called “Ants2Whale.” The site for this version of AppleJeus is ants2whale[.]com (Acquire Infrastructure: Domain [T1583.001]). The website shows a legitimate-looking cryptocurrency company and application. The website contains multiple spelling and grammar mistakes indicating the creator may not have English as a first language. The website states that to download Ants2Whale, a user must contact the administrator, as their product is a “premium package” (Develop Capabilities: Malware [T1587.001]).

The domain ants2whale[.]com resolved to IP address 198.54.114[.]237 from September 23, 2020, to January 22, 2021. The IP address is controlled by NameCheap, Inc. (ASN 22612) and is located in Atlanta, GA. This IP address is in the same ASN for CoinGoTrade[.]com and Dorusio[.]com.

The domain ants2whale[.]com had a valid Sectigo SSL certificate (Obtain Capabilities: Digital Certificates [T1588.004]). The SSL certificate was “Domain Control Validated,” a weak security verification level that does not require validation of the owner’s identity or the actual business’s existence.

Ants2Whale Application Analysis Windows Program

As of late 2020, the Windows program was not available on VirusTotal. It is likely very similar to the macOS X version detailed below.

macOS X Program

The macOS version of the malicious application is a DMG Installer. The installer looks legitimate and has very similar functionality to the Windows version, but it does not have a digital certificate and will warn the user of that before installation. The installer executes the following actions.

  • Installs Ants2Whale in folder /Applications/Ants2whale.app/Contents/MacOS/Ants2whale
  • Installs Ants2WhaleHelper in folder /Library/Application Support/Ants2WhaleSupport/
  • Executes a postinstall script
    • Moves com.Ants2whale.pkg.wallet.plist to folder /Library/LaunchDaemons/
    • Runs Ants2WhaleHelper in the background

The Ants2Whale and Ants2WhaleHelper programs and the postinstall script function almost identically to previous versions of AppleJeus and will not be discussed in depth in this advisory.

For more details on AppleJeus Version 7: Ants2Whale, see MAR-10322463-7.v1.

ATT&CK Profile

Figure 2 and table 2 provide summaries of the MITRE ATT&CK techniques observed.

Figure 2: MITRE ATT&CK enterprise techniques used by AppleJeus

 

Table 2: MITRE ATT&CK techniques observed

Tactic Title Technique ID Technique Title Resource Development [TA0042] T1583.001 Acquire Infrastructure: Domain Resource Development [TA0042] T1583.006 Acquire Infrastructure: Web Services Resource Development [TA0042] T1587.001 Develop Capabilities: Malware Resource Development [TA0042] T1588.003 Obtain Capabilities: Code Signing Certificates Resource Development [TA0042] T1588004 Obtain Capabilities: Digital Certificates Initial Access [TA0001] T1566.002 Phishing: Spearphishing Link Execution [TA0002] T1059 Command and Scripting Interpreter Execution [TA0002] T1059.002 Command and Scripting Interpreter: AppleScript Execution [TA0002] T1204.002 User Execution: Malicious File Persistence [TA0003] T1053.004 Scheduled Task/Job: Launchd Persistence [TA0003] T1543.004 Create or Modify System Process: Launch Daemon Persistence [TA0003] T1547 Boot or Logon Autostart Execution Privilege Escalation [TA0004] T1053.005 Scheduled Task/Job: Scheduled Task Defense Evasion [TA0005] T1027 Obfuscated Files or Information Defense Evasion [TA0005] T1548 Abuse Elevation Control Mechanism Defense Evasion [TA0005] T1564.001 Hide Artifacts: Hidden Files and Directories Discovery [TA0007] T1033 System Owner/User Discovery Exfiltration [TA0010] T1041 Exfiltration Over C2 Channel Command and Control [TA0011] T1071.001

Application Layer Protocol: Web Protocols

Command and Control [TA0011] T1573 Encrypted Channel Command and Control [TA0011] T1573.001 Encrypted Channel: Symmetric Cryptography MitigationsCompromise Mitigations

Organizations that identify AppleJeus malware within their networks should take immediate action. Initial actions should include the following steps.

  • Contact the FBI, CISA, or Treasury immediately regarding any identified activity related to AppleJeus. (Refer to the Contact Information section below.)
  • Initiate your organization’s incident response plan.
  • Generate new keys for wallets, and/or move to new wallets.
  • Introduce a two-factor authentication solution as an extra layer of verification.  
  • Use hardware wallets, which keep the private keys in a separate, secured storage area.
  • To move funds out off a compromised wallet:
    • Do not use the malware listed in this advisory to transfer funds, and  
    • Form all transactions offline and then broadcast them to the network all at once in a short online session, ideally prior to the attacker accessing them.
  • Remove impacted hosts from network.
  • Assume the threat actors have moved laterally within the network and downloaded additional malware.
  • Change all passwords to any accounts associated with impacted hosts.
  • Reimage impacted host(s).  
  • Install anti-virus software to run daily deep scans of the host.
  • Ensure your anti-virus software is setup to download the latest signatures daily.
  • Install a Host Based Intrusion Detection (HIDS)-based software and keep it up to date.
  • Ensure all software and hardware is up to date, and all patches have been installed.
  • Ensure network-based firewall is installed and/or up to date.
  • Ensure the firewall’s firmware is up to date.
Pro-Active Mitigations

Consider the following recommendations for defense against AppleJeus malware and related activity.

Cryptocurrency Users
  • Verify source of cryptocurrency-related applications.
  • Use multiple wallets for key storage, striking the appropriate risk balance between hot and cold storage.
  • Use custodial accounts with multi-factor authentication mechanisms for both user and device verification.
  • Patronize cryptocurrency service businesses that offer indemnity protections for lost or stolen cryptocurrency.
  • Consider having a dedicated device for cryptocurrency management.
Financial Service Companies Cryptocurrency Businesses All Organizations
  • Incorporate IOCs identified in CISA’s Malware Analysis Reports on https://us-cert.cisa.gov/northkorea into intrusion detection systems and security alert systems to enable active blocking or reporting of suspected malicious activity.
  • See table 3 below, which provides a summary of preventative ATT&CK mitigations based on observed techniques.

Table 3: MITRE ATT&CK mitigations based on observed techniques

Mitigation Description User Training [M1017] Train users to identify social engineering techniques and spearphishing emails. User Training [M1017] Provide users with the awareness of common phishing and spearphishing techniques and raise suspicion for potentially malicious events. User Account Management [M1018] Limit privileges of user accounts and remediate Privilege Escalation vectors so only authorized administrators can create new Launch Daemons. User Account Management [M1018] Limit privileges of user accounts and remediate Privilege Escalation vectors so only authorized administrators can create scheduled tasks on remote systems. SSL/TLS Inspection [M1020] Use SSL/TLS inspection to see encrypted sessions’ contents to look for network-based indicators of malware communication protocols. Restrict Web-Based Content [M1021] Determine if certain websites that can be used for spearphishing are necessary for business operations and consider blocking access if the activity cannot be monitored well or poses a significant risk. Restrict Web-Based Content [M1021] Block Script extensions to prevent the execution of scripts and HTA files that may commonly be used during the exploitation process. Restrict Web-Based Content [M1021] Employ an adblocker to prevent malicious code served up through ads from executing. Restrict File and Directory Permissions [M1022] Prevent all users from writing to the /Library/StartupItems directory to prevent any startup items from getting registered since StartupItems are deprecated. Privileged Account Management [M1026] When PowerShell is necessary, restrict PowerShell execution policy to administrators. Be aware that there are methods of bypassing the PowerShell execution policy, depending on environment configuration. Privileged Account Management [M1026] Configure the Increase Scheduling Priority option only to allow the Administrators group the rights to schedule a priority process. Operating System Configuration [M1028] Configure settings for scheduled tasks to force tasks to run under the authenticated account’s context instead of allowing them to run as SYSTEM. Network Intrusion Prevention [M1031] Use network intrusion detection and prevention systems that use network signatures to identify traffic for specific adversary malware and mitigate activity at the network level. Execution Prevention [M1038] Use application control tools where appropriate. Execution Prevention [M1038] Use application control tools to prevent the running of executables masquerading as other files. Behavior Prevention on Endpoint [M1040] Configure endpoint (if possible) to block some process injection types based on common sequences of behavior during the injection process. Disable or Remove Feature or Program [M1042] Disable or remove any unnecessary or unused shells or interpreters. Code Signing [M1045] Where possible, only permit the execution of signed scripts. Code Signing [M1045] Require that a trusted developer I.D. sign all AppleScript before being executed to subject AppleScript code to the same scrutiny as other .app files passing through Gatekeeper. Audit [M1047] Audit logging for launchd events in macOS can be reviewed or centrally collected using multiple options, such as Syslog, OpenBSM, or OSquery. Audit [M1047] Toolkits like the PowerSploit framework contain PowerUp modules that can be used to explore systems for permission weaknesses in scheduled tasks that could be used to escalate privileges. Antivirus/Antimalware [M1049] Use an antivirus program to quarantine suspicious files automatically.

 

Contact Information

Recipients of this report are encouraged to contribute any additional information that they may have related to this threat.

For any questions related to this report or to report an intrusion and request resources for incident response or technical assistance, please contact:

References Revisions
  • February 17, 2021: Initial Version

This product is provided subject to this Notification and this Privacy & Use policy.

2021. február 11.

AA21-042A: Compromise of U.S. Water Treatment Facility

Original release date: February 11, 2021
Summary

On February 5, 2021, unidentified cyber actors obtained unauthorized access to the supervisory control and data acquisition (SCADA) system at a U.S. drinking water treatment plant. The unidentified actors used the SCADA system’s software to increase the amount of sodium hydroxide, also known as lye, a caustic chemical, as part of the water treatment process. Water treatment plant personnel immediately noticed the change in dosing amounts and corrected the issue before the SCADA system’s software detected the manipulation and alarmed due to the unauthorized change. As a result, the water treatment process remained unaffected and continued to operate as normal. The cyber actors likely accessed the system by exploiting cybersecurity weaknesses, including poor password security, and an outdated operating system. Early information indicates it is possible that a desktop sharing software, such as TeamViewer, may have been used to gain unauthorized access to the system. Onsite response to the incident included Pinellas County Sheriff Office (PCSO), U.S. Secret Service (USSS), and the Federal Bureau of Investigation (FBI).

The FBI, the Cybersecurity and Infrastructure Security Agency (CISA), the Environmental Protection Agency (EPA), and the Multi-State Information Sharing and Analysis Center (MS-ISAC) have observed cyber criminals targeting and exploiting desktop sharing software and computer networks running operating systems with end of life status to gain unauthorized access to systems. Desktop sharing software, which has multiple legitimate uses—such as enabling telework, remote technical support, and file transfers—can also be exploited through malicious actors’ use of social engineering tactics and other illicit measures. Windows 7 will become more susceptible to exploitation due to lack of security updates and the discovery of new vulnerabilities. Microsoft and other industry professionals strongly recommend upgrading computer systems to an actively supported operating system. Continuing to use any operating system within an enterprise beyond the end of life status may provide cyber criminals access into computer systems.

Click here for a PDF version of this report.

Technical DetailsDesktop Sharing Software

The FBI, CISA, EPA, and MS-ISAC have observed corrupt insiders and outside cyber actors using desktop sharing software to victimize targets in a range of organizations, including those in the critical infrastructure sectors. In addition to adjusting system operations, cyber actors also use the following techniques:

  • Use access granted by desktop sharing software to perform fraudulent wire transfers.
  • Inject malicious code that allows the cyber actors to
    • Hide desktop sharing software windows,
    • Protect malicious files from being detected, and
    • Control desktop sharing software startup parameters to obfuscate their activity.
  • Move laterally across a network to increase the scope of activity.

TeamViewer, a desktop sharing software, is a legitimate popular tool that has been exploited by cyber actors engaged in targeted social engineering attacks, as well as large scale, indiscriminate phishing campaigns. Desktop sharing software can also be used by employees with vindictive and/or larcenous motivations against employers.

Beyond its legitimate uses, TeamViewer allows cyber actors to exercise remote control over computer systems and drop files onto victim computers, making it functionally similar to Remote Access Trojans (RATs). TeamViewer’s legitimate use, however, makes anomalous activity less suspicious to end users and system administrators compared to RATs.

Windows 7 End of Life

On January 14, 2020, Microsoft ended support for the Windows 7 operating system, which includes security updates and technical support unless certain customers purchased an Extended Security Update (ESU) plan. The ESU plan is paid per-device and available for Windows 7 Professional and Enterprise versions, with an increasing price the longer a customer continues use. Microsoft will only offer the ESU plan until January 2023. Continued use of Windows 7 increases the risk of cyber actor exploitation of a computer system.

Cyber actors continue to find entry points into legacy Windows operating systems and leverage Remote Desktop Protocol (RDP) exploits. Microsoft released an emergency patch for its older operating systems, including Windows 7, after an information security researcher discovered an RDP vulnerability in May 2019. Since the end of July 2019, malicious RDP activity has increased with the development of a working commercial exploit for the vulnerability. Cyber actors often use misconfigured or improperly secured RDP access controls to conduct cyberattacks. The xDedic Marketplace, taken down by law enforcement in 2019, flourished by compromising RDP vulnerabilities around the world.

MitigationsGeneral Recommendations

The following cyber hygiene measures may help protect against the aforementioned scheme:

  • Update to the latest version of the operating system (e.g., Windows 10).
  • Use multiple-factor authentication.
  • Use strong passwords to protect Remote Desktop Protocol (RDP) credentials.
  • Ensure anti-virus, spam filters, and firewalls are up to date, properly configured, and secure.
  • Audit network configurations and isolate computer systems that cannot be updated.
  • Audit your network for systems using RDP, closing unused RDP ports, applying multiple-factor authentication wherever possible, and logging RDP login attempts.
  • Audit logs for all remote connection protocols.
  • Train users to identify and report attempts at social engineering.
  • Identify and suspend access of users exhibiting unusual activity.
Water and Wastewater Systems Security Recommendations

The following physical security measures serve as additional protective measures:

  • Install independent cyber-physical safety systems. These are systems that physically prevent dangerous conditions from occurring if the control system is compromised by a threat actor.
  • Examples of cyber-physical safety system controls include:
    • Size of the chemical pump
    • Size of the chemical reservoir
    • Gearing on valves
    • Pressure switches, etc.

The benefit of these types of controls in the water sector is that smaller systems, with limited cybersecurity capability, can assess their system from a worst-case scenario. The operators can take physical steps to limit the damage. If, for example, cyber actors gain control of a sodium hydroxide pump, they will be unable to raise the pH to dangerous levels.

TeamViewer Software Recommendations

For a more secured implementation of TeamViewer software:

  • Do not use unattended access features, such as “Start TeamViewer with Windows” and “Grant easy access.”
  • Configure TeamViewer service to “manual start,” so that the application and associated background services are stopped when not in use.
  • Set random passwords to generate 10-character alphanumeric passwords.
  • If using personal passwords, utilize complex rotating passwords of varying lengths. Note: TeamViewer allows users to change connection passwords for each new session. If an end user chooses this option, never save connection passwords as an option as they can be leveraged for persistence.
  • When configuring access control for a host, utilize custom settings to tier the access a remote party may attempt to acquire.
  • Require remote party to receive confirmation from the host to gain any access other than “view only.” Doing so will ensure that, if an unauthorized party is able to connect via TeamViewer, they will only see a locked screen and will not have keyboard control.
  • Utilize the ‘Block and Allow’ list which enables a user to control which other organizational users of TeamViewer may request access to the system. This list can also be used to block users suspected of unauthorized access.
Contact Information

To report suspicious or criminal activity related to information found in this Joint Cybersecurity Advisory, contact your local FBI field office at www.fbi.gov/contact-us/field, or the FBI’s 24/7 Cyber Watch (CyWatch) at (855) 292-3937 or by e-mail at CyWatch@fbi.gov or your local WMD Coordinator. When available, please include the following information regarding the incident: date, time, and location of the incident; type of activity; number of people affected; type of equipment used for the activity; the name of the submitting company or organization; and a designated point of contact.

To request incident response resources or technical assistance related to these threats, contact CISA at Central@cisa.dhs.gov.

Revisions
  • February 11, 2021: Initial Version

This product is provided subject to this Notification and this Privacy & Use policy.

2021. január 8.

AA21-008A: Detecting Post-Compromise Threat Activity in Microsoft Cloud Environments

Original release date: January 8, 2021
Summary

This Advisory uses the MITRE Adversarial Tactics, Techniques, and Common Knowledge (ATT&CK®) framework. See the ATT&CK for Enterprise for all referenced threat actor tactics and techniques.

This Alert is a companion alert to AA20-352A: Advanced Persistent Threat Compromise of Government Agencies, Critical Infrastructure, and Private Sector Organizations. AA20-352A primarily focuses on an advanced persistent threat (APT) actor’s compromise of SolarWinds Orion products as an initial access vector into networks of U.S. Government agencies, critical infrastructure entities, and private network organizations. As noted in AA20-352A, the Cybersecurity and Infrastructure Security Agency (CISA) has evidence of initial access vectors in addition to the compromised SolarWinds Orion products.

This Alert also addresses activity—irrespective of the initial access vector leveraged—that CISA attributes to an APT actor. Specifically, CISA has seen an APT actor using compromised applications in a victim’s Microsoft 365 (M365)/Azure environment. CISA has also seen this APT actor utilizing additional credentials and Application Programming Interface (API) access to cloud resources of private and public sector organizations. These tactics, techniques, and procedures (TTPs) feature three key components:

  • Compromising or bypassing federated identity solutions;
  • Using forged authentication tokens to move laterally to Microsoft cloud environments; and
  • Using privileged access to a victim’s cloud environment to establish difficult-to-detect persistence mechanisms for Application Programming Interface (API)-based access.

This Alert describes these TTPs and offers an overview of, and guidance on, available open-source tools—including a CISA-developed tool, Sparrow—for network defenders to analyze their Microsoft Azure Active Directory (AD), Office 365 (O365), and M365 environments to detect potentially malicious activity.

Note: this Alert describes artifacts—presented by these attacks—from which CISA has identified detectable evidence of the threat actor’s initial objectives. CISA continues to analyze the threat actor’s follow-on objectives.

Technical Details

Frequently, CISA has observed the APT actor gaining Initial Access [TA0001] to victims’ enterprise networks via compromised SolarWinds Orion products (e.g., Solorigate, Supernova).[1] However, CISA is investigating instances in which the threat actor may have obtained initial access by Password Guessing [T1110.001], Password Spraying [T1110.003], and/or exploiting inappropriately secured administrative or service credentials (Unsecured Credentials [T1552]) instead of utilizing the compromised SolarWinds Orion products.

CISA observed this threat actor moving from user context to administrator rights for Privilege Escalation [TA0004] within a compromised network and using native Windows tools and techniques, such as Windows Management Instrumentation (WMI), to enumerate the Microsoft Active Directory Federated Services (ADFS) certificate-signing capability. This enumeration allows threat actors to forge authentication tokens (OAuth) to issue claims to service providers—without having those claims checked against the identity provider—and then to move laterally to Microsoft Cloud environments (Lateral Movement [TA0008]).

The threat actor has also used on-premises access to manipulate and bypass identity controls and multi-factor authentication. This activity demonstrates how sophisticated adversaries can use credentials from one portion of an organization to move laterally (Lateral Movement [TA0008]) through trust boundaries, evade defenses and detection (Defense Evasion [TA0005]), and steal sensitive data (Collection [TA0009]).

This level of compromise is challenging to remediate and requires a rigorous multi-disciplinary effort to regain administrative control before recovering.

MitigationsDetection

Guidance on identifying affected SolarWinds software is well documented.[2] However—once an organization identifies a compromise via SolarWinds Orion products or other threat actor TTPs—identifying follow-on activity for on-premises networks requires fine-tuned network and host-based forensics.

The nature of cloud forensics is unique due to the growing and rapidly evolving technology footprints of major vendors. Microsoft's O365 and M365 environments have built-in capabilities for detecting unusual activity. Microsoft also provides premium services (Advanced Threat Protection [ATP] and Azure Sentinel), which enable network defenders to investigate TTPs specific to the Solorigate activity.[3]

Detection Tools

CISA is providing examples of detection tools for informational purposes only. CISA does not endorse any commercial product or service, including any subjects of analysis. Any reference to specific commercial products, processes, or services does not constitute or imply their endorsement, recommendation, or favoring by CISA.

There are a number of open-source tools available to investigate adversary activity in Microsoft cloud environments and to detect unusual activity, service principals, and application activity.[4] Publicly available PowerShell tools that network defenders can use to investigate M365 and Microsoft Azure include:

  • CISA's Sparrow,
  • Open-source utility Hawk, and
  • CrowdStrike's Azure Reporting Tool (CRT).

Additionally, Microsoft's Office 365 Management API and Graph API provide an open interface for ingesting telemetry and evaluating service configurations for signs of anomalous activity and intrusion.

Note: these open-source tools are highlighted and explained to assist with on-site investigation and remediation in cloud environments but are not all-encompassing. Open source tools can be complemented by services such as Azure Sentinel, a Microsoft premium service that provides comprehensive analysis tools, including custom detections for the activity indicated.

General Guidance on Using Detection Tools
  1. Audit the creation and use of service principal credentials. Look for unusual application usage, such as use of dormant applications.
  2. Audit the assignment of credentials to applications that allow non-interactive sign-in by the application. Look for unexpected trust relationships added to the Azure Active Directory.
  3. Download the interactive sign-ins from the Azure admin portal or use the Microsoft Sentinel product. Review new token validation time periods with high values and investigate whether it was a legitimate change or an attempt to gain persistence by a threat actor.
Sparrow

CISA created Sparrow to help network defenders detect possible compromised accounts and applications in the Azure/M365 environment. The tool focuses on the narrow scope of user and application activity endemic to identity- and authentication-based attacks seen recently in multiple sectors. It is neither comprehensive nor exhaustive of available data. It is intended to narrow a larger set of available investigation modules and telemetry to those specific to recent attacks on federated identity sources and applications.

CISA advises Sparrow users to take the following actions.

  1. Use Sparrow to detect any recent domain authentication or federation modifications.
    1. Domain and federation modification operations are uncommon and should be investigated.
  2. Examine logs for new and modified credentials applied to applications and service principals; delineate for the credential type. Sparrow can be used to detect the modification of service principals and application credentials.
    1. Create a timeline for all credential changes, focusing on recent wholesale changes.
    2. Review the “top actors” for activity in the environment and the number of credential modifications performed.
    3. Monitor changes in application and service principal credentials.
    4. Investigate any instances of excessive permissions being granted, including, but not limited to, Exchange Online, Microsoft Graph, and Azure AD Graph.
  3. Use Sparrow to detect privilege escalation, such as adding a service principal, user, or group to a privileged role.
  4. Use Sparrow to detect OAuth consent and users’ consent to applications, which is useful for interpreting changes in adversary TTPs.
  5. Use Sparrow to identify anomalous Security Assertion Markup Language (SAML) token sign-ins by pivoting on the unified audit log UserAuthenticationValue of 16457, which is an indicator of how a SAML token was built and is a potential indicator for forged SAML tokens.
    1. Note that this TTP has not been the subject of significant published security research but may indicate an unusual usage of a token, such as guest access for external partners to M365 resources.
  6. Review the PowerShell logs that Sparrow exports.
    1. Review PowerShell mailbox sign-ins and validate that the logins are legitimate actions.
    2. Review PowerShell usage for users with PowerShell in the environment.
  7. Use Sparrow to check the Graph API application permissions of all service principals and applications in M365/Azure AD.
    1. Investigate unusual activity regarding Microsoft Graph API permissions (using either the legacy https://graph.windows.net/ or https://graph.microsoft.com). Graph is used frequently as part of these TTPs, often to access and manipulate mailbox resources.
  8. Review Sparrow’s listed tenant’s Azure AD domains, to see if the domains have been modified.
  9. For customers with G5 or E5 licensing levels, review MailItemsAccessed for insight into what application identification (ID) was used for accessing users’ mailboxes. Use Sparrow to query for a specific application ID using the app id investigation capability, which will check to see if it is accessing mail or file items.
    1. The MailItemsAccessed event provides audibility for mailbox data accessed via mail protocols or clients.
    2. By analyzing the MailItemsAccessed action, incident responders can determine which user mailbox items have been accessed and potentially exfiltrated by a threat actor. This event will be recorded even in some situations where the message was not necessarily read interactively (e.g., bind or sync).[5]
    3. The resulting suspicious application ID can provide incident responders with a pivot to detect other suspicious applications that require additional analysis.
    4. Check for changes to applications with regards to the accessing of resources such as mail or file items.
Hawk

Hawk is an open-source, PowerShell-driven, community-developed tool network defenders can use to quickly and easily gather data from O365 and Azure for security investigations. Incident responders and network defenders can investigate specific user principals or the entire tenant. Data it provides include IP addresses and sign-in data. Additionally, Hawk can track IP usage for concurrent login situations.

Hawk users should review login details for administrator accounts and take the following steps.

  1.  Investigate high-value administrative accounts to detect anomalous or unusual activity (Global Admins).
  2. Enable PowerShell logging, and evaluate PowerShell activity in the environment not used for traditional or expected purposes.
    1. PowerShell logging does not reveal the exact cmdlet that was run on the tenant.
  3. Look for users with unusual sign-in locations, dates, and times.
  4. Check permissions of service principals and applications in M365/Azure AD.
  5. Detect the frequency of resource access from unusual places. Use the tool to pivot to a trusted application and see if it is accessing mail or file items.
  6. Review mailbox rules and recent mailbox rule changes.
CrowdStrike Azure Reporting Tool

CrowdStrike's Azure Reporting Tool (CRT) can help network defenders analyze their Microsoft Azure AD and M365 environment to help organizations analyze permissions in their AzureAD tenant and service configuration. This tool has minor overlap with Sparrow; it shows unique items, but it does not cover the same areas. CISA is highlighting this tool because it is one of the only free, open-source tools available to investigate this activity and could be used to complement Sparrow.

Detection Tool Distinctions
  • Sparrow differs from CRT by looking for specific indicators of compromise associated with the recent attacks.
  • CRT focuses on the tenant’s Azure AD permissions and Exchange Online configuration settings instead of the unified audit log, which gives it a different output from Sparrow or Hawk.
  • CRT returns the same broad scope of application/delegated permissions for service principals and applications as Hawk.
  • As part of its investigation, Sparrow homes in on a narrow set of application permissions given to the Graph API, which is common to the recent attacks.
  • CRT looks at Exchange Online federation configuration and federation trust, while Sparrow focuses on listing Azure AD domains.
  • Among the items network defenders can use CRT to review are delegated permissions and application permissions, federation configurations, federation trusts, mail forwarding rules, service principals, and objects with KeyCredentials.
Detection Methods

Microsoft breaks the threat actor’s recent activity into four primary stages, which are described below along with associated detection methods. Microsoft describes these stages as beginning with all activity after the compromise of the on-premises identity solution, such as ADFS.[6]

Note: this step provides an entry vector to cloud technology environments, and is unnecessary when the threat actor has compromised an identity solution or credential that allows the APT direct access to the cloud(e.g., without leveraging the SolarWinds Orion vulnerability).

Stage 1: Forging a trusted authentication token used to access resources that trust the on-premises identity provider

These attacks (often referred to as “Golden Security Assertion Markup Language” attacks) can be analyzed using a combination of cloud-based and standard on-premises techniques.[7] For example, network defenders can use OAuth claims for specific principals made at the Azure AD level and compare them to the on-premises identity.

Export sign-in logs from the Azure AD portal and look at the Authentication Method field.

Note: at portal.azure.com, click on a user and review the authentication details (e.g., date, method, result). Without Sentinel, this is the only way to get these logs, which are critical for this effort.

Detection Method 1: Correlating service provider login events with corresponding authentication events in Active Directory Federation Services (ADFS) and Domain Controllers

Using SAML single sign-on, search for any logins to service providers that do not have corresponding event IDs 4769, 1200, and 1202 in the domain.

Detection Method 2: Identifying certificate export events in ADFS

Look for:

  1. The IP address and Activity_ID in EventCode 410 and the Activity_ID and Instance_ID in EventCode 500.
  2. Export-PfxCertificate or certutil-exportPFX in Event IDs 4103 and 4104, which may include detection of a certificate extraction technique.
  3. Deleted certificate extraction with ADFSdump performed using Sysmon Event ID 18 with the pipe name \microsoft##wid\tsql\query (exclude processes regularly making this pipe connection on the machine).
  4. Event ID 307 (The Federation Service configuration was changed), which can be correlated to relevant Event ID 510 with the same instance ID for change details (Event ID 510 with the same Instance ID could be more than one event per single Event ID 307 event).

Detection Method 3: Customizing SAML response to identify irregular access

This method serves as prevention for the future (and would only detect future, not past, activity), as it helps identify irregularities from the point of the change forward. Organizations can modify SAML responses to include custom elements for each service provider to monitor and detect any anomalous requests.[8]

Detection Method 4: Detecting malicious ADFS trust modification

A threat actor who gains administrative access to ADFS can add a new, trusted ADFS rather than extracting the certificate and private key as part of a standard Golden SAML attack.[9]
Network defenders should look for:

  1. Event ID 307 (The Federation Service configuration was changed), which can be correlated to relevant Event ID 510 with the same Instance ID for change details. (Event ID 510 with the same Instance ID could be more than one event per single Event ID 307 event.)
    1. Review events, particularly searching for Configuration: Type: IssuanceAuthority where Property Value references an unfamiliar domain.
  2. Possible activity of an interrogating ADFS host by using ADFS PowerShell plugins. Look for changes in the federation trust environment that would indicate new ADFS sources.

Stage 2: Using the forged authentication token to create configuration changes in the Service Provider, such as AzureAD (establishing a foothold)

After the threat actor has compromised the on-premises identity provider, they identify their next series of objectives by reviewing activity in the Microsoft Cloud activity space (Microsoft Azure and M365 tenants).

The threat actor uses the ability to forge authentication tokens to establish a presence in the cloud environment. The actor adds additional credentials to an existing service principal. Once the threat actor has impersonated a privileged AzureAD account, they are likely to further manipulate the Azure/M365 environment (action on objectives in the cloud).

Network defenders should take the following steps.

  1. Audit the creation and use of service principal and application credentials. Sparrow will detect modifications to these credentials.
    1. Look for unusual application usage, such as dormant or forgotten applications being used again.
    2. Audit the assignment of credentials to applications that allow non-interactive sign-in by the application.
  2. Look for unexpected trust relationships that have been added to AzureAD. (Download the last 30 days of non-interactive sign-ins from the Azure portal or use Azure Sentinel.).[10]
  3. Use Hawk (and any sub-modules available) to run an investigation on a specific user. Hawk will provide IP addresses, sign-in data, and other data. Hawk can also track IP usage in concurrent login situations.
  4. Review login details for administrator accounts (e.g., high-value administrative accounts, such as Global Admins). Look for unusual sign-in locations, dates, and times.
  5. Review new token validation time periods with high values and investigate whether the changes are legitimate or a threat actor’s attempts to gain persistence.

Stage 3: Acquiring an OAuth access token for the application using the forged credentials added to an existing application or service principal and calling APIs with the permissions assigned to that application

In some cases, the threat actor has been observed adding permissions to existing applications or service principals. Additionally the actor has been seen establishing new applications or service principals briefly and using them to add permissions to the existing applications or service principals, possibly to add a layer of indirection (e.g., using it to add a credential to another service principal, and then deleting it).[11]

Network defenders should use Sparrow to:

  1. Examine highly privileged accounts; specifically using sign-in logs, look for unusual sign-in locations, dates, and times.
  2. Create a timeline for all credential changes.
  3. Monitor changes in application credentials (the script will export into csv named AppUpdate_Operations_Export).
  4. Detect service principal credentials change and service principal change (e.g., if an actor adds new permissions or expands existing permissions).
    1. Export and view this activity via the ServicePrincipal_Operations_Export.
  5. Record OAuth consent and consent to applications
    1. Export and view this record via the Consent_Operations_Export file.
  6. Investigate instances of excessive high permissions, including, but not limited to Exchange Online, Microsoft Graph, and Azure AD Graph.
    1. Review Microsoft Graph API permissions granted to service principals.
    2. Export and view this activity via the ApplicationGraphPermissions csv file.
      1. Note: Hawk can also return the full list of service principal permissions for further investigation.
    3. Review top actors and the amount of credential modifications performed.
    4. Monitor changes in application credentials.
  7. Identify manipulation of custom or third-party applications.
    1. Network defenders should review the catalog of custom or third-party vendors with applications in the Microsoft tenant and perform the above interrogation principles on those applications and trusts.
  8. Review modifications to federation trust settings.
    1. Review new token validation time periods with high values and investigate whether this was a legitimate change or an attempt to gain persistence by the threat actor.
      1. The script detects the escalation of privileges, including the addition of Service Principals (SP) to privileged roles. Export this data into csv called AppRoleAssignment_Operations_Export.

Stage 4: Once access has been established, the threat actor Uses Microsoft Graph API to conduct action on objectives from an external RESTful API (queries impersonating existing applications).

Network defenders should:

  1. In MailItemsAccessed  operations, found within the Unified Audit Log (UAL), review the application ID used (requires G5 or E5 license for this specific detail).
  2. Query the specific application ID, using the Sparrow script’s app ID investigation capability to interrogate mail and file items accessed for that applicationID (Use the application ID utility for any other suspicious apps that require additional analysis.).
  3. Check the permissions of an application in M365/AzureAD using Sparrow.
    1. Hawk will return Azure_Application_Audit, and Sparrow will return ApplicationGraphPermissions.
    2. Network defenders will see the IP address that Graph API uses.
    3. Note: the Microsoft IP address may not show up as a virtual private server/anonymized endpoint.
  4. Investigate a specific service principal, if it is a user-specific user account, in Hawk. This activity is challenging to see without Azure Sentinel or manually downloading and reviewing logs from the sign-in portal.
Microsoft Telemetry Nuances

The existing tools and techniques used to evaluate cloud-based telemetry sources present challenges not represented in traditional forensic techniques. Primarily, the amount of telemetry retention is far less than the traditional logging facilities of on-premises data sources. Threat actor activity that is more than 90 days old is unlikely to have been saved by traditional sources or be visible with the Microsoft M365 Management API or in the UAL.

Service principal logging is available using the Azure Portal via the "Service Principal Sign-ins" feature. Enable settings in the Azure Portal (see “Diagnostic Setting”) to ingest logs into Sentinel or a third-party security information and event management (SIEM) tool. An Azure Premium P1 or Premium P2 license is necessary to access this setting as well as other features, such as a log analytics workspace, storage account, or event hub.[12] These logs must be downloaded manually if not ingested by one of the methods listed in the Detection Methods section.

Global Administrator rights are often required by tools other than Hawk and Sparrow to evaluate M365 cloud security posture. Logging capability and visibility of data varies by licensing models and subscription to premium services, such as Microsoft Defender for O365 and Azure Sentinel. According to CrowdStrike, "There was an inability to audit via API, and there is the requirement for global admin rights to view important information which we found to be excessive. Key information should be easily accessible."[13]

Documentation for specific event codes, such as UserAuthenticationMethod 16457, which may indicate a suspicious SAML token forgery, is no longer available in the M365 Unified Access Log. Auditing narratives on some events no longer exist as part of core Microsoft documentation sources.

The use of industry-standard SIEMs for log detection is crucial for providing historical context for threat hunting in Microsoft cloud environments. Standard G3/E3 licenses only provide 90 days of auditing; with the advanced auditing license that is provided with a G5/E5 license, audit logs can be extended to retain information for a year. CISA notes that this license change is proactive, rather than reactive: it allows enhanced visibility and features for telemetry from the moment of integration but does not provide retroactive visibility on previous events or historical context.

A properly configured SIEM can provide:

  1. Longer term storage of log data.
  2. Cross correlation of log data with endpoint data and network data (such as those produced by ADFS servers), endpoint detection and response data, and identity provider information.
  3. Ability to query use of application connectors in Azure.

Built-in tools, such as Microsoft Cloud Services and M365 applications, provide much of the same visibility available from custom tools and are mapped to the MITRE ATT&CK framework and easy-to-understand dashboards.[14] However, these tools often do not have the ability to pull historical data older than seven days. Therefore, storage solutions that appropriately meet governance standards and usability metrics for analysts for the SIEM must be carefully planned and arranged.

Contact Information

CISA encourages recipients of this report to contribute any additional information that they may have related to this threat. For any questions related to this report, please contact CISA at

  • 1-888-282-0870 (From outside the United States: +1-703-235-8832)
  • central@cisa.dhs.gov (UNCLASS)
  • us-cert@dhs.sgov.gov (SIPRNET)
  • us-cert@dhs.ic.gov (JWICS)

CISA encourages you to report any suspicious activity, including cybersecurity incidents, possible malicious code, software vulnerabilities, and phishing-related scams. Reporting forms can be found on the CISA/US-CERT homepage at http://www.us-cert.cisa.gov/.

Resources

Azure Active Directory Workbook to Assess Solorigate Risk: https://techcommunity.microsoft.com/t5/azure-active-directory-identity/azure-ad-workbook-to-help-you-assess-solorigate-risk/ba-p/2010718

Volexity - Dark Halo Leverages SolarWinds Compromise to Breach Organizations: https://www.volexity.com/blog/2020/12/14/dark-halo-leverages-solarwinds-compromise-to-breach-organizations/

How to Find Activity with Sentinel: https://www.verboon.info/2020/10/monitoring-service-principal-sign-ins-with-azuread-and-azure-sentinel/

Third-Party Walkthrough of the Attack: https://dirkjanm.io/azure-ad-privilege-escalation-application-admin/

National Security Agency Advisory on Detecting Abuse of Authentication Mechanisms: https://media.defense.gov/2020/Dec/17/2002554125/-1/-1/0/AUTHENTICATION_MECHANISMS_CSA_U_OO_198854_20.PDF

Microsoft 365 App for Splunk: https://splunkbase.splunk.com/app/3786/

CISA Remediation Guidance: https://us-cert.cisa.gov/ncas/alerts/aa20-352a

Feedback

CISA strives to make this report a valuable tool for our partners and welcomes feedback on how this publication could be improved. You can help by answering a few short questions about this report at the following URL: https://www.us-cert.cisa.gov/forms/feedback.

References Revisions
  • Initial version: January 8, 2021

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