VxTrivial46

Hunt Hypothesis

This detection identifies files matching the VxTrivial46 YARA signature, which often indicates the presence of benign or legacy software components that may be leveraged by adversaries for initial foothold establishment. Proactively hunting for this indicator within Azure Sentinel allows the SOC team to distinguish between expected baseline noise and potential early-stage reconnaissance activities before they escalate into more complex threats.

YARA Rule

rule VxTrivial46
{
      meta:
		author="malware-lu"
strings:
		$a0 = { B4 4E B1 20 BA [2] CD 21 BA [2] B8 ?? 3D CD 21 }

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: The Microsoft Defender for Endpoint (MDE) or CrowdStrike Falcon agent performs its daily scheduled signature update and heuristic scan, which involves the temporary extraction of large compressed archives containing YARA signatures. This activity often triggers VxTrivial46 due to the high volume of file I/O and pattern matching on system directories like C:\ProgramData\Microsoft\Windows Defender.

  • Suggested Filter: Exclude processes where the executable path matches *\\Windows Defender\\MpCmdRun.exe or *\\CrowdStrike\\csfalcon.exe AND the parent process is a scheduled task service (svchost.exe -k LocalService).

• Scenario: An automated backup job executed by Veeam Backup & Replication or Commvault initiates a full scan of the file system to index new data, causing the YARA engine to match against thousands of newly created temporary files in the C:\Temp directory.

  • Suggested Filter: Create an exclusion for any detection where the file extension is .tmp, .vbk, or .log AND the process name contains VeeamTransportService.exe or CommServeAgent.exe.

• Scenario: The IT operations team runs a PowerShell script (Update-SystemConfig.ps1) to deploy configuration updates across 50+ workstations, which involves unzipping and parsing XML/JSON policy files that match the rule’s signature for specific embedded patterns.

  • Suggested Filter: Exclude detections where the parent process is powershell.exe AND the command line arguments contain -ExecutionPolicy Bypass or a known internal script hash (e.g., Hash: SHA256-...).

• Scenario: The enterprise Document Management System (e.g., SharePoint Online or On-Premises) triggers a content indexer that scans user-uploaded documents in the network share, generating multiple