VxInvoluntary1349

Hunt Hypothesis

This detection identifies potential malicious activity where a process exhibits involuntary behavior patterns matching the specific signature defined by the VxInvoluntary1349 YARA rule, often indicative of fileless attacks or memory-resident threats. Proactively hunting for this signal in Azure Sentinel allows the SOC team to uncover low-severity anomalies that may represent early-stage lateral movement or evasion tactics before they escalate into critical incidents.

YARA Rule

rule VxInvoluntary1349
{
      meta:
		author="malware-lu"
strings:
		$a0 = { BA [2] B9 [2] 8C DD ?? 8C C8 ?? 8E D8 8E C0 33 F6 8B FE FC [2] AD ?? 33 C2 AB }

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 the VxInvoluntary1349 detection rule, including suggested filters and exclusions tailored for an enterprise environment:

• Scenario: Microsoft Endpoint Configuration Manager (SCCM/MECM) Client Service (ccmexec.exe) initiating a background process to perform health checks or software updates.

  • Context: The SCCM client frequently spawns child processes or modifies registry keys in the HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\CCM path, which can mimic involuntary execution patterns detected by YARA.
  • Suggested Filter/Exclusion: Create an exclusion rule for the parent process ccmexec.exe running under the system account (NT AUTHORITY\SYSTEM) where the file path matches C:\Program Files (x86)\Microsoft Configuration Manager\*.

• Scenario: Scheduled Windows Defender Antivirus scans triggering real-time protection modules.

  • Context: During peak hours, the Windows Defender service (MsMpEng.exe) often launches auxiliary scanning engines or updates definition databases, generating file system events that match the rule’s signature for involuntary process creation.
  • Suggested Filter/Exclusion: Exclude processes where the parent is MsMpEng.exe and the command line contains keywords like “Scan”, “Update”, or “RealTime”. Specifically, filter out events occurring between 02:00 and 04:00 UTC when scheduled maintenance jobs are active.

• Scenario: Automated backup agents (e.g., Veeam Backup & Replication) performing incremental backups on file servers.

  • Context: The Veeam Agent (VeeamAgent.exe) or the Veeam Transport service often spawns temporary worker processes to handle data streaming, which can be flagged as unexpected process behavior by the YARA rule.
  • **Suggested Filter/