StealthPEv11

Hunt Hypothesis

This rule detects the presence of the StealthPEv11 YARA signature, which typically identifies specific malicious or suspicious executable files associated with low-level stealth mechanisms or known threat actor tooling. Proactively hunting for this indicator in Azure Sentinel allows the SOC team to identify compromised endpoints or dormant payloads that may evade standard behavioral detections, ensuring early containment of stealthy threats within the environment.

YARA Rule

rule StealthPEv11
{
      meta:
		author="malware-lu"
strings:
		$a0 = { BA [3] 00 FF E2 BA [3] 00 B8 [4] 89 02 83 C2 03 B8 [4] 89 02 83 C2 FD FF E2 }

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

• Legitimate Antivirus/EDR Self-Scanning or Update: Many modern EDR agents (e.g., CrowdStrike Falcon, Carbon Black, Defender for Endpoint) use in-memory scanning or heuristic analysis that can temporarily mask PE headers or use stealthy loading techniques to avoid detection by other security tools.

  • Filter/Exclusion: Exclude processes where the parent process is a known EDR agent (e.g., FalconSensor.exe, cb.exe, MsMpEng.exe) and the file path resides in the vendor’s installation directory (e.g., C:\Program Files\CrowdStrike\, C:\Program Files\Microsoft Security Client\).

• Just-In-Time (JIT) Compilation by .NET or Java Applications: Applications using JIT compilers (e.g., dotnet.exe, java.exe, node.exe) generate native code in memory at runtime. If the YARA rule inspects the process memory or loaded modules, the dynamically generated code may lack standard PE signatures or exhibit “stealthy” characteristics that trigger the rule.

  • Filter/Exclusion: Exclude processes where the executable name is a known JIT host (dotnet.exe, java.exe, node.exe, v8.exe) and the parent process is a standard application launcher or service host (svchost.exe, services.exe).

• Scheduled Backup or Snapshot Jobs: Enterprise backup tools (e.g., Veeam, Commvault, Windows Server Backup) often use volume shadow copies or direct I/O to capture disk states. During this process, they may load PE files into memory with specific flags or use stealthy file handles to prevent locking, which can mimic stealthy PE loading behavior.

  • Filter/Exclusion: Exclude processes where the command line contains backup-related keywords (e.g., --snapshot, shadowcopy, backup) and the parent