StonesPEEncryptorv20

Hunt Hypothesis

This rule detects the presence of PE files encrypted by the StonesPEEncryptor v2.0, a tool frequently used by threat actors to obfuscate malicious payloads and evade static analysis. Proactively hunting for this indicator in Azure Sentinel allows the SOC to identify compromised endpoints or staging areas where adversaries are preparing executables for deployment, enabling early intervention before the encrypted payload is executed.

YARA Rule

rule StonesPEEncryptorv20
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 53 51 52 56 57 55 E8 [4] 5D 81 ED 42 30 40 ?? FF 95 32 35 40 ?? B8 37 30 40 ?? 03 C5 2B 85 1B 34 40 ?? 89 85 27 34 40 ?? 83 }

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: A developer or DevOps engineer uses the Stones PE encryptor tool (or a wrapper script invoking it) to obfuscate a custom C/C++ executable for a specific internal microservice or agent that requires lightweight protection against simple reverse engineering.

  • Filter/Exclusion: Exclude files located in specific development build directories (e.g., C:\Projects\InternalTools\Builds\) or exclude processes where the parent process is a known compiler/IDE (e.g., msbuild.exe, code.exe, devenv.exe) and the file extension is .exe or .dll within a designated source control workspace.

• Scenario: A security team or application owner uses the StonesPEEncryptor to create a protected version of a legacy line-of-business application for distribution to a specific client or partner, storing the encrypted binary in a shared network drive or staging folder.

  • Filter/Exclusion: Exclude files located in known staging or distribution shares (e.g., \\fileserver\dist\, \\fileserver\staging\) or exclude files that are read-only and have a specific custom extension (e.g., .enc, .protected) rather than standard executable extensions, if the YARA rule can be tuned to check file attributes or naming conventions.

• Scenario: An automated CI/CD pipeline job uses a custom build step that invokes the StonesPEEncryptor to obfuscate a release candidate binary before uploading it to an artifact repository (e.g., Artifactory, Nexus, or S3 bucket).

  • Filter/Exclusion: Exclude processes where the parent process is a CI/CD agent (e.g., jenkins-agent.exe, gitlab-runner.exe, azure-pipelines-agent.exe) or exclude files in temporary build directories (e.g., C:\jenkins\workspace\, `C:\