Armadillo300aSiliconRealmsToolworks

Hunt Hypothesis

This rule detects the presence of the Armadillo 300a malware variant, a known threat actor tool that often leverages custom tooling for initial access or lateral movement within Azure environments. Proactively hunting for this specific YARA signature allows the SOC to identify dormant or low-fidelity implantations that may evade standard behavioral detections, ensuring early containment of targeted infrastructure compromises.

YARA Rule

rule Armadillo300aSiliconRealmsToolworks
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 60 E8 00 00 00 00 5D 50 51 EB 0F ?? EB 0F ?? EB 07 ?? EB 0F ?? EB 08 FD EB 0B F2 EB F5 EB F6 F2 EB 08 FD EB E9 F3 EB E4 FC ?? 59 58 50 51 EB 0F ?? EB 0F ?? EB 07 ?? EB 0F ?? EB 08 FD EB 0B F2 EB F5 EB F6 F2 EB 08 FD EB E9 F3 EB E4 FC ?? 59 58 50 51 EB 0F }

condition:
		$a0 at pe.entry_point
}

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 developer or DevOps engineer runs a local build pipeline or CI/CD agent (e.g., Jenkins, GitLab Runner, or Azure DevOps Agent) that compiles C/C++ code using GCC or Clang. The resulting binary may contain specific string literals or section headers that match the YARA rule’s pattern, particularly if the rule targets common compiler artifacts or specific library names (like libstdc++ or libc references) often found in debug builds.

  • Filter/Exclusion: Exclude files located in standard build directories (e.g., C:\builds\, /tmp/build/, D:\ci\) or exclude files with extensions like .exe or .dll that are owned by service accounts running build agents (e.g., svc-jenkins, svc-gitlab-runner).

• Scenario: An IT administrator installs or updates a proprietary vendor tool (e.g., a backup client like Veeam, a monitoring agent like Datadog, or a security tool like CrowdStrike Falcon) that bundles static libraries or uses specific compiler flags. The YARA rule might match on unique string patterns or section names introduced by the vendor’s build process, especially if the rule was designed to catch a specific malware variant that mimics common tooling.

  • Filter/Exclusion: Exclude files in vendor-specific installation directories (e.g., C:\Program Files\Veeam\, C:\Program Files\Datadog\, C:\Program Files\CrowdStrike\) or exclude files signed by known vendor certificates (e.g., Veeam Software, Datadog, Inc., CrowdStrike, Inc.).

• Scenario: A system administrator performs a disk cleanup or temporary file deletion task using a tool like cleanmgr or a custom PowerShell script that moves or copies temporary build artifacts or log