Gamarue_Andromeda

Hunt Hypothesis

The Gamarue_Andromeda detection rule identifies potential command and control (C2) activity associated with the Gamarue family of malware, which may indicate initial compromise or lateral movement within a network. SOC teams should proactively hunt for this behavior in Azure Sentinel to detect early-stage malware activity and prevent further exploitation in their environment.

YARA Rule

rule Worm_Gamarue 
{

    meta:
        author = "Centro Criptológico Nacional (CCN)"
        ref = "https://www.ccn-cert.cni.es/informes/informes-ccn-cert-publicos.html"
        description = "Gamarue_Andromeda"       

    strings:
        $a = { 69 E1 2A B0 2D 80 44 E3 2D 80 44 E3 2D 80 44 E3 EE 8F 1B E3 2A 80 44 E3 EE 8F 19 E3 3A 80 44 E3 2D 80 45 E3 CD 81 44 E3 0A 46 39 E3 34 80 44 E3 0A 46 29 E3 A5 80 44 E3 0A 46 2A E3 5C 80 44 E3 0A 46 36 E3 2C 80 44 E3 0A 46 3C E3 2C 80 44 E3 }
    condition:
        $a 
}

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 1 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Scenario: A system administrator is using PowerShell to automate the deployment of a legitimate application that includes a script with a similar file name or string as the malware.

  Filter/Exclusion: Exclude processes initiated by powershell.exe where the command line includes known legitimate deployment scripts or paths (e.g., C:\Deployment\Script.ps1).

• Scenario: A scheduled job runs Task Scheduler to execute a legitimate batch file that temporarily creates a file with a name similar to the malware.

  Filter/Exclusion: Exclude tasks initiated by schtasks.exe with a known legitimate job name or path (e.g., C:\ScheduledTasks\UpdateScript.bat).

• Scenario: A security tool like Windows Defender or Microsoft Defender ATP performs a scan and generates temporary files with names similar to the malware.

  Filter/Exclusion: Exclude processes with the parent process msdefender.exe or MsMpEng.exe and check for known security tool artifacts.

• Scenario: A developer is using Visual Studio or MSBuild to compile a project that includes a file with a name similar to the malware due to a naming convention.

  Filter/Exclusion: Exclude processes initiated by devenv.exe or msbuild.exe and check for known development tool directories (e.g., C:\Projects\MyApp\).

• Scenario: A system update or patching tool like Windows Update or WSUS temporarily creates files with names similar to the malware during installation.

  Filter/Exclusion: Exclude processes initiated by wusa.exe or wsusutil.exe and check for known update directories (e.g., C:\Windows\Temp\ or C:\Windows\SoftwareDistribution\).