EXEShieldv01bv03bv03SMoKE

Hunt Hypothesis

This rule identifies potentially obfuscated or packed executable files by matching specific structural patterns, which adversaries often use to evade static analysis and hide malicious payloads. Proactively hunting for these artifacts in Azure Sentinel allows the SOC to uncover stealthy malware or trojans that may have bypassed initial perimeter defenses and are executing within the environment.

YARA Rule

rule EXEShieldv01bv03bv03SMoKE
{
      meta:
		author="malware-lu"
strings:
		$a0 = { E8 04 00 00 00 83 60 EB 0C 5D EB 05 }

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 is running a local build pipeline or CI/CD agent (e.g., Jenkins, GitLab Runner, or Azure DevOps Agent) that compiles C/C++ code into a native executable. The YARA rule likely matches common compiler artifacts, linker symbols, or specific string patterns (like “SMOKE” or version strings) embedded in the resulting .exe file during the build process.

  • Filter/Exclusion: Exclude files located in standard build directories (e.g., C:\builds\, C:\workspaces\, C:\temp\) or exclude processes where the parent process is a known build tool (e.g., msbuild.exe, cmake.exe, make.exe, dotnet.exe).

• Scenario: An IT administrator is deploying or updating a specific vendor application that includes a “smoke test” utility or a diagnostic module named with the “SMOKE” prefix (e.g., SmokeTest.exe, smoke_check.dll) for post-installation validation. The YARA rule may be triggering on the filename or internal strings related to this diagnostic component.

  • Filter/Exclusion: Exclude files whose names contain smoke (case-insensitive) if they are located in vendor-specific installation directories (e.g., C:\Program Files\VendorApp\diagnostics\) or if the parent process is a known installer (e.g., msiexec.exe, setup.exe, install.exe).

• Scenario: A security team or QA engineer is manually executing a custom “smoke test” script or executable to verify network connectivity, service availability, or basic functionality after a patch deployment. This custom tool might be a small, unsigned .exe that contains specific markers or strings matching the YARA rule’s patterns.

  • Filter/Exclusion: