XCRv013

Hunt Hypothesis

This detection identifies specific file artifacts matching the XCRv013 YARA signature to uncover potential early-stage adversary activity that may not trigger standard alert thresholds. Proactively hunting for this pattern in Azure Sentinel allows the SOC team to validate low-severity indicators before they escalate into more significant incidents, ensuring comprehensive coverage of subtle threat behaviors.

YARA Rule

rule XCRv013
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 93 71 08 [8] 8B D8 78 E2 [4] 9C 33 C3 [4] 60 79 CE [4] E8 01 [4] 83 C4 04 E8 AB FF FF FF [4] 2B E8 [4] 03 C5 FF 30 [4] C6 ?? EB }

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 5 specific false positive scenarios for detection rule XCRv013, including targeted filters and exclusions suitable for an enterprise environment:

• Scenario: Scheduled Antivirus Definition Updates

  • Context: The YARA signature triggers when the central management server pushes new virus definition updates to endpoints. Tools like Microsoft Defender for Endpoint or Symantec Endpoint Protection often extract compressed update packages containing executable payloads that match XCRv013 patterns during the nightly maintenance window (e.g., 2:00 AM – 4:00 AM).
  • Filter/Exclusion: Create a time-based exclusion for the specific process MpCmdG.exe (Microsoft) or SymantecDefender.exe running on the domain controller subnet between 01:00 and 05:00 UTC. Alternatively, exclude file paths matching C:\ProgramData\Microsoft\Windows Defender\Updates\Temp.

• Scenario: Automated Software Deployment via SCCM

  • Context: During enterprise-wide application rollouts using Microsoft Endpoint Configuration Manager (MECM/SCCM), the deployment agent (ccmsetup.exe) extracts installation packages. If XCRv013 detects specific embedded scripts or installers within these packages, it generates alerts for every deployed machine during business hours.
  • Filter/Exclusion: Exclude alerts where the parent process is WUAUENG.exe (Windows Update) or ccmexec.exe. Additionally, add a rule to suppress alerts if the file hash matches known good hashes stored in the SCCM content library for the specific application being deployed.

• Scenario: Backup Agent Data Compression and Encryption

  • Context: Enterprise backup solutions like Veeam Backup & Replication or Commvault frequently create temporary compressed archives (.vbk, `.b