Carbanak Malware

Hunt Hypothesis

Carbanak Malware is likely being used to exfiltrate sensitive data through covert network communication channels. SOC teams should proactively hunt for this behavior in Azure Sentinel to detect and mitigate advanced persistent threat activity before significant data loss occurs.

YARA Rule

rule Carbanak_0915_3
{

    meta:
        description = "Carbanak Malware"
        author = "Florian Roth"
        reference = "https://www.csis.dk/en/csis/blog/4710/"
        date = "2015-09-03"
        score = 70

    strings:
        $s1 = "wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww" fullword ascii
        $s2 = "SHInvokePrinterCommandA" fullword ascii
        $s3 = "Ycwxnkaj" fullword ascii

    condition:
        uint16(0) == 0x5a4d and filesize < 700KB and all of them
}

Deployment Notes

This YARA rule can be deployed in the following contexts:

• Microsoft Defender for Endpoint — Custom indicators / advanced hunting
• Email Gateway — Attachment scanning
• File Share Monitoring — Periodic scanning of shared drives
• YARA CLI — Manual threat hunting on endpoints

This rule contains 3 string patterns in its detection logic.

References

• https://www.csis.dk/en/csis/blog/4710/
• Source Rule

False Positive Guidance

• Scenario: Scheduled System Maintenance Task
  Description: A legitimate system maintenance task, such as Task Scheduler running a script to clean temporary files or update system settings.
  Filter/Exclusion: Exclude tasks with TaskName containing “Cleanup”, “Update”, or “Maintenance” and with User set to a service account or system account.

• Scenario: Admin Performing Remote Desktop Session
  Description: An administrator using Remote Desktop Protocol (RDP) to access a server and perform routine administrative tasks.
  Filter/Exclusion: Exclude connections where User is a known admin account and ProcessName is mstsc.exe or rdpclip.exe.

• Scenario: Database Backup Job Execution
  Description: A scheduled SQL Server backup job using sqlbackup.exe or sqlcmd.exe to back up databases.
  Filter/Exclusion: Exclude processes where CommandLine contains BACKUP DATABASE or sqlbackup.exe with a known backup schedule name.

• Scenario: PowerShell Script for Patch Management
  Description: A PowerShell script running via PowerShell.exe to apply patches or update software, such as using Windows Update or Chocolatey.
  Filter/Exclusion: Exclude processes where CommandLine contains Update-AppxProvisionedPackage, choco, or wuauclt.exe.

• Scenario: Log File Analysis by SIEM Tool
  Description: A Security Information and Event Management (SIEM) tool, such as Splunk or ELK Stack, analyzing log files for security events.
  Filter/Exclusion: Exclude processes where ProcessName is splunkd.exe, logstash, or elasticsearch and CommandLine contains log analysis commands.