PEArmor049Hying

Hunt Hypothesis

This hypothesis targets the execution of obfuscated or packed Windows executables that exhibit specific binary characteristics, potentially indicating an adversary is using packing techniques to evade static analysis and signature-based detection. Proactively hunting for these artifacts in Azure Sentinel allows the SOC team to identify suspicious processes or files that may be hiding malicious payloads, thereby reducing the risk of undetected initial access or lateral movement activities.

YARA Rule

rule PEArmor049Hying
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 56 52 51 53 55 E8 15 01 00 00 32 [2] 00 00 00 00 00 }

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: A developer or DevOps engineer runs the dotnet build or msbuild command to compile a C# application, which invokes the .NET compiler (csc.exe) or related tooling that may interact with PE headers or perform basic integrity checks during the assembly generation process.
  • Filter/Exclusion: Exclude processes where the parent process is MSBuild.exe, dotnet.exe, or csc.exe, or where the command line contains arguments like /t:build or /restore.
• Scenario: An enterprise antivirus or endpoint detection and response (EDR) agent (e.g., CrowdStrike Falcon, SentinelOne, or Microsoft Defender for Endpoint) performs a real-time scan or on-demand full system scan, reading PE files to check for known signatures or anomalies, potentially triggering heuristic or header-based YARA rules.
  • Filter/Exclusion: Exclude processes associated with known security tools such as FalconSensor.exe, SentinelOneAgent.exe, MsMpEng.exe, or Defender.exe, or exclude file paths under C:\Program Files\CrowdStrike\ or C:\Program Files\SentinelOne\.
• Scenario: A scheduled task or service (e.g., vssadmin.exe for Volume Shadow Copy, or wbadmin.exe for Windows Backup) creates or restores a system image, which involves reading and writing PE files (executables and DLLs) and may temporarily alter or validate PE structures during the backup/restore process.
  • Filter/Exclusion: Exclude processes named vssadmin.exe, wbadmin.exe, or wbengine.exe, or exclude file paths under C:\Windows\System32\ when the parent process is a backup-related service.
• Scenario: A software installer (e.g., msiexec.exe