VxACMEClonewarMutant

Hunt Hypothesis

This detection identifies potential malware variants that mimic legitimate ACME applications to evade signature-based defenses through polymorphic behavior. A proactive hunt is essential in Azure Sentinel to uncover these stealthy clones before they establish persistence or exfiltrate sensitive data within the cloud environment.

YARA Rule

rule VxACMEClonewarMutant
{
      meta:
		author="malware-lu"
strings:
		$a0 = { FC AD 3D FF FF 74 20 E6 42 8A C4 E6 42 E4 61 0C 03 E6 61 AD B9 40 1F E2 FE }

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

Here are 4 specific false positive scenarios for the VxACMEClonewarMutant detection rule, including suggested filters and exclusions:

• Scenario: Automated Backup Agent File Cloning

  • Context: The enterprise uses Veeam Backup & Replication or Rubrik agents running on file servers. These agents frequently clone large database files (e.g., .vmdk, .bak) to a staging area before compression, creating near-identical binary structures that mimic the “mutant” signature of the rule.
  • Suggested Filter/Exclusion: Exclude processes matching VeeamTransportSvc.exe and rubrik-agent.exe from the detection logic. Additionally, add a path exclusion for directories named \BackupStaging\ or \TempClone\.

• Scenario: Scheduled Antivirus Definition Updates

  • Context: During nightly maintenance windows (e.g., 02:00 UTC), Microsoft Defender for Endpoint or Symantec Endpoint Protection downloads and unpacks new definition packs. The extraction process often creates temporary files that are binary clones of the original compressed payload, triggering the rule’s mutation detection logic.
  • Suggested Filter/Exclusion: Create a time-based exclusion window (e.g., 01:30–04:30 UTC) for processes named MsMpEng.exe and SymantecDefenderCore. Alternatively, exclude file extensions .cab, .zip, and .dat generated by these specific vendors.

• Scenario: Software Deployment via Configuration Management

  • Context: The IT operations team utilizes Microsoft SCCM (Configuration Manager) or Ansible to push application updates. When deploying a patch, the system creates a “cloned” version of the installer executable in a temporary deployment folder before execution,