VxGRUNT2Family

Hunt Hypothesis

This detection identifies potential malware activity from the VxGRUNT2 family by matching file signatures against a specialized YARA rule within Azure Sentinel logs. Proactively hunting for this behavior allows the SOC team to uncover early-stage infections that may exhibit low severity initially but could evolve into significant threats if left unaddressed in the cloud environment.

YARA Rule

rule VxGRUNT2Family
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 48 E2 F7 C3 51 53 52 E8 DD FF 5A 5B 59 C3 B9 00 00 E2 FE C3 }

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 VxGRUNT2Family detection rule in an enterprise environment, along with suggested filters:

• Scenario: Automated Endpoint Protection Scans

  • Context: The VxGRUNT family often exhibits behavior similar to legitimate security agents. In environments using CrowdStrike Falcon or Microsoft Defender for Endpoint, the background scanning service (C:\Program Files\CrowdStrike\csagent.exe or C:\Windows\System32\mpcmdrun.exe) may generate file artifacts or network connections that match the YARA signature’s heuristic patterns.
  • Suggested Filter: Exclude processes where the executable path contains known security vendor directories (e.g., \CrowdStrike\, \Microsoft Defender\, \Symantec\) and the process name matches standard agent binaries (csagent.exe, mpcmdrun.exe, rtvscan64.exe).

• Scenario: Scheduled Software Deployment via SCCM

  • Context: During off-hours, System Center Configuration Manager (SCCM) or Microsoft Intune pushes application updates. The deployment agent (ccmexec.exe) often unpacks temporary files or executes installers that contain code structures resembling the VxGRUNT family’s modular architecture, triggering a match on the extracted payload.
  • Suggested Filter: Create an exclusion for events where the parent process is ccmexec.exe (SCCM) and the event source indicates a “Software Update” or “Application Deployment” job ID, specifically filtering out temporary directory paths like C:\Windows\CCMCache\.

• Scenario: Legacy Backup Agent Operations

  • Context: Enterprise backup solutions such as Veeam Backup & Replication or Commvault utilize proprietary agents that compress and encrypt data streams. The VxGRUNT rule may mis