SimplePack12build3009Method2bagie

Hunt Hypothesis

This YARA rule targets specific memory patterns associated with the SimplePack packer, indicating the presence of obfuscated executables that adversaries often use to evade static analysis and signature-based detection. Proactively hunting for these artifacts in Azure Sentinel allows the SOC team to identify low-severity, stealthy payloads that may be staging for further compromise or executing persistent mechanisms within the environment.

YARA Rule

rule SimplePack12build3009Method2bagie
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 4D 5A 90 EB 01 00 52 E9 86 01 00 00 50 45 00 00 4C 01 02 00 00 00 00 00 00 00 00 00 00 00 00 00 E0 00 0F 03 0B 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0C 00 00 00 00 [3] 00 10 00 00 00 02 00 00 01 00 00 00 00 00 00 00 04 00 00 00 00 00 00 00 }

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 build engineer runs the SimplePack compiler or linker (specifically build 3009) as part of a continuous integration (CI) pipeline or local build script to generate application binaries. The YARA rule matches the specific version string or method signature embedded in the executable or intermediate object files.
  • Filter/Exclusion: Exclude processes where the parent process is a known build tool (e.g., msbuild.exe, dotnet.exe, npm.exe, or jenkins-agent) and the file path resides in standard development directories (e.g., C:\Users\Public\Documents\Visual Studio 2022\Projects\ or C:\Jenkins\workspace\).
• Scenario: An IT administrator deploys a custom internal utility or patching tool that was compiled using the SimplePack framework (build 3009) for efficient packaging of configuration files or scripts. The tool is executed via a scheduled task or Group Policy Object (GPO) software installation.
  • Filter/Exclusion: Exclude execution if the binary is located in a trusted administrative tools directory (e.g., C:\Program Files\CorpTools\ or C:\Admin\Scripts\) and the parent process is svchost.exe (for GPO) or Taskeng.exe (for scheduled tasks).
• Scenario: A third-party application installer or updater (e.g., for a niche industry-specific software like CAD or financial modeling tools) uses SimplePack build 3009 to unpack or verify its own components during the installation or update process.
  • Filter/Exclusion: Exclude if the process name matches known installer executables (e.g., setup.exe, install.exe, unins000.exe) and the working directory is within a temporary installation folder