PEBundlev02v20x

Hunt Hypothesis

This hypothesis targets the presence of PE bundle executables, which adversaries often use to obfuscate malicious payloads or stage components of a multi-stage attack within a single file. Proactively hunting for these bundles in Azure Sentinel helps identify hidden persistence mechanisms or initial access artifacts that may evade standard signature-based detections due to their low severity and complex structure.

YARA Rule

rule PEBundlev02v20x
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 9C 60 E8 02 [3] 33 C0 8B C4 83 C0 04 93 8B E3 8B 5B FC 81 EB [2] 40 ?? 87 DD 6A 04 68 ?? 10 [2] 68 ?? 02 [2] 6A ?? FF 95 }

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: Execution of the Windows Resource Hacker or 7-Zip to extract resources from a .exe or .dll file. These tools often manipulate the PE header or bundle resources in a way that mimics the structural anomalies detected by the PEBundlev02v20x rule, particularly if the binary is being repacked or inspected in a staging directory.

  • Filter/Exclusion: Exclude files located in specific developer or staging directories (e.g., C:\Dev\, C:\Temp\, C:\Users\<Admin>\Downloads\) where the parent process is a known archiver or resource editor (e.g., 7z.exe, ResourceHacker.exe, Notepad++).

• Scenario: Visual Studio Code or JetBrains IDEs launching a bundled Node.js runtime or Python interpreter for extension hosting or language servers. These IDEs often use custom-built or bundled runtimes that may have non-standard PE section alignments or import tables, triggering the “bundled” or “modified PE” heuristic.

  • Filter/Exclusion: Exclude processes where the parent process is Code.exe (VS Code), idea64.exe (IntelliJ), or pycharm64.exe, and the file path resides within the application’s node_modules or plugins directory.

• Scenario: Sysinternals Suite tools (specifically Process Monitor or Process Explorer) analyzing a target executable. When these tools load or inspect a PE file, they may temporarily modify memory-mapped views or create temporary copies with altered headers, which can be misidentified as a bundled or tampered PE by the YARA rule if the scan occurs during active analysis.

  • Filter/Exclusion: Exclude files where the parent process is ProcMon.exe or `Proc