PEProtect09byCristophGabler1998

Hunt Hypothesis

This rule identifies Windows executables packed with PEProtect, a commercial packer frequently abused by threat actors to obscure code and evade static analysis. Proactively hunting for these packed binaries in Azure Sentinel helps detect low-severity anomalies or stealthy malware that may be leveraging packing techniques to hide malicious payloads within the environment.

YARA Rule

rule PEProtect09byCristophGabler1998
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 50 45 2D 50 52 4F 54 45 43 54 20 30 2E 39 }

condition:
		$a0
}

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 legacy Windows application (e.g., an older version of Adobe Acrobat Reader or a specific industrial control system client) uses a custom, non-standard PE header structure or packing technique that mimics the specific byte patterns defined in the PEProtect09 rule, causing the YARA scanner to match the file during a routine antivirus or endpoint detection scan.

  • Filter/Exclusion: Add an exclusion for the specific executable path (e.g., C:\Program Files\LegacyApp\app.exe) in the YARA scanning policy or the EDR agent configuration, ensuring the exclusion is scoped to the specific file hash or path rather than the entire directory to minimize risk.

• Scenario: A development team uses a custom build script or a specific compiler plugin (e.g., a modified version of MSVC or a custom linker) that injects a specific marker or padding sequence into the PE header for internal versioning or debugging purposes, which coincidentally matches the PEProtect09 signature.

  • Filter/Exclusion: Create a YARA exclusion rule that matches the specific build artifact name or directory (e.g., *.dll in C:\Builds\Release\) and tag these files with a custom attribute (e.g., build_artifact) in the EDR console to allow for quick suppression of alerts on these known internal binaries.

• Scenario: A scheduled maintenance job runs a utility like Sysinternals' strings` or a custom C++ tool that reads and writes PE files in memory or on disk, and the tool’s own binary or a temporary file it creates has a header structure that triggers the rule due to the specific alignment or section names used by the tool.

  • Filter/Exclusion: Exclude the specific process name (e.g., strings.exe or custom_pe_tool.exe) from the YARA scanning