VxIgor

Hunt Hypothesis

This hunt hypothesis targets adversary behavior where attackers deploy VxIgor malware to establish persistence and silently exfiltrate sensitive data within the Azure Sentinel environment. Proactive hunting is essential because this rule operates at a low severity level, meaning initial detections may lack sufficient context for immediate alerting but require deeper investigation to uncover potential long-term compromise or lateral movement.

YARA Rule

rule VxIgor
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 1E B8 CD 7B CD 21 81 FB CD 7B 75 03 E9 87 00 33 DB 0E 1F 8C }

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 3-5 specific false positive scenarios for the VxIgor detection rule in an enterprise environment, including suggested filters or exclusions:

• Scenario: Automated Backup Agents Scanning Legacy Archives

  • Context: Enterprise backup solutions like Veeam Backup & Replication or Commvault often scan large legacy archives (e.g., .zip, .tar) containing historical logs. The VxIgor YARA rule may match specific byte signatures within these compressed archives that resemble the malware’s header structure, triggering alerts during nightly backup windows.
  • Filter/Exclusion: Exclude file paths matching C:\Program Files\Veeam\Backup and D:\Commvault\ContentStore. Additionally, add a filter to ignore files with extensions .vbk, .v2dx, or .zip if the parent process is Veeam.Backup.Service.exe or commserver.exe.

• Scenario: Endpoint Protection Scanning of Software Installers

  • Context: During mass deployment cycles, tools like Microsoft Intune, SCCM (Configuration Manager), or Jamf push software installers (.msi, .exe) to endpoints. The VxIgor rule may flag the installer executables themselves as malicious because they contain embedded compression libraries or digital certificate structures similar to VxIgor’s persistence mechanisms.
  • Filter/Exclusion: Create a whitelist for processes running under ccmsetup.exe, intunagent.exe, or jamf.exe. Configure the rule to suppress alerts where the file hash matches known good installers stored in the enterprise asset inventory database, specifically targeting files located in C:\Windows\CCM\ and C:\ProgramData\Microsoft Intune Management Extension.

• Scenario: Scheduled PowerShell Scripts for System Maintenance

  • Context: