PEBundlev310

Hunt Hypothesis

This rule targets the execution of PE files that have been bundled or packed using specific v3.10 techniques, a common method adversaries employ to obscure code logic and evade static analysis. Proactively hunting for these signatures in Azure Sentinel allows the SOC to identify potentially obfuscated payloads early in the kill chain, reducing the risk of undetected malicious activity in cloud-hosted workloads.

YARA Rule

rule PEBundlev310
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 9C 60 E8 02 00 00 00 33 C0 8B C4 83 C0 04 93 8B E3 8B 5B FC 81 EB 07 20 40 00 87 DD [4] 40 00 01 }

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 developer or DevOps engineer uses a legitimate software bundler (e.g., Inno Setup, NSIS, or WiX Toolset) to create a custom installer package for an internal application. The resulting executable often contains a PE header structure that matches the “bundled” characteristics targeted by the rule, especially if the bundler embeds standard system DLLs or uses a specific compression algorithm that mimics the pattern.

  • Filter/Exclusion: Exclude files located in known build output directories (e.g., C:\Builds\, C:\Artifacts\) or whitelist executables signed by the organization’s internal code-signing certificate. Additionally, exclude files with names ending in .setup.exe or .install.exe if they are generated by known build pipelines.

• Scenario: An IT administrator runs a standard Windows utility like msiexec.exe or wusa.exe to install or update a patch, or uses dotnet-install.ps1 / dotnet.exe to deploy the .NET runtime. These tools often extract or bundle components into temporary directories, and the intermediate executable or the runtime host itself may exhibit PE characteristics that trigger the “bundled” heuristic, particularly if the rule inspects the import table or section entropy.

  • Filter/Exclusion: Whitelist the specific binary paths for standard Windows installers (e.g., C:\Windows\System32\msiexec.exe, C:\Windows\System32\wusa.exe) and the .NET runtime host (C:\Program Files\dotnet\dotnet.exe). Exclude files in temporary directories (%TEMP%, C:\Windows\Temp) if the parent process is a known system installer.

• Scenario: A security team or application owner uses a tool like 7z.exe (