EncryptPE12003518WFS

Hunt Hypothesis

This YARA rule targets specific Portable Executable (PE) files that exhibit characteristics of encrypted or packed code, potentially indicating the presence of obfuscated malware or trojans designed to evade static analysis. Proactively hunting for these artifacts in Azure Sentinel allows the SOC to identify stealthy payloads that may be executing on endpoints or stored in cloud storage, ensuring early detection of threats that rely on code encryption to hide their functionality.

YARA Rule

rule EncryptPE12003518WFS
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 60 9C 64 FF 35 00 00 00 00 E8 79 }

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

• Antivirus/EDR Real-Time Scanning of Portable Executables: When an endpoint protection agent (e.g., CrowdStrike Falcon, Microsoft Defender for Endpoint, or SentinelOne) performs a real-time scan on a newly downloaded or compiled .exe file, it may temporarily apply an encryption or obfuscation layer to the file in memory or on disk during the analysis phase. This can cause the YARA rule to match the encrypted PE header.
  • Filter/Exclusion: Exclude processes from known EDR/AV service accounts (e.g., CrowdStrike Falcon Service, MsMpEng.exe, SentinelOne Service) or filter out events where the parent process is a known security agent.
• Software Packaging and Installer Creation: When developers or IT operations use tools like Inno Setup, NSIS, or WiX Toolset to build installers, these tools often compress or encrypt the internal PE binaries within the installer package. If the YARA rule is scanning the installer file itself (which contains encrypted PE sections) rather than the extracted executable, it will trigger a false positive.
  • Filter/Exclusion: Exclude files with extensions common to installers (.msi, .exe with specific installer signatures) or filter based on the parent process being a known packaging tool (e.g., ISCC.exe for Inno Setup, makensis for NSIS).
• Application Virtualization and Sandboxing: Enterprise application virtualization tools like App-V (Microsoft Application Virtualization), Thincast, or Fusion often store applications in virtualized containers where the PE headers may be encrypted or obfuscated to prevent tampering or to enforce license compliance. When these virtualized apps are launched, the underlying PE file on disk may appear encrypted.
  • Filter/Exclusion: Exclude paths under known virtualization directories (