PolyEnEV001LennartHedlund

Hunt Hypothesis

This rule targets the execution of the PolyEnEV001LennartHedlund payload, a known polyglot executable often associated with initial access or web shell deployment, by identifying its unique binary signature in memory or on disk. Proactively hunting for this indicator in Azure Sentinel helps SOC teams detect stealthy, low-severity intrusions that may bypass traditional network-based detections and establish a foothold within the environment.

YARA Rule

rule PolyEnEV001LennartHedlund
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 50 6F 6C 79 45 6E 45 00 4D 65 73 73 61 67 65 42 6F 78 41 00 55 53 45 52 33 32 2E 64 6C 6C }

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 software developer is running a local build pipeline that uses CMake or MSBuild to compile a C++ project containing embedded version strings or resource files matching the LennartHedlund signature (often associated with specific legacy codebases or open-source libraries).
  • Filter/Exclusion: Exclude processes originating from build tools such as cmake.exe, msbuild.exe, or dotnet.exe when the parent process is a development IDE (e.g., devenv.exe, code.exe) or a CI/CD agent (e.g., agent.exe for Azure DevOps, runner.exe for GitLab CI).
• Scenario: An IT administrator is deploying a patch or configuration script using PowerShell that invokes a custom utility or library named after the developer (e.g., LennartHedlund.dll or a script referencing the name) for internal tooling or legacy application maintenance.
  • Filter/Exclusion: Exclude events where the command line contains powershell.exe or pwsh.exe and the working directory is within known administrative paths (e.g., C:\AdminTools\, C:\Scripts\) or the user account belongs to the Domain Admins or IT_Ops group.
• Scenario: A QA engineer is executing a regression test suite using Selenium or Playwright that loads a test fixture or mock server component containing the specific string pattern, potentially in a temporary directory or test data folder.
  • Filter/Exclusion: Exclude processes where the parent is a browser driver (e.g., chromedriver.exe, geckodriver.exe) or test runner (e.g., pytest.exe, mocha.exe) and the file path contains keywords like test, fixture, mock, or `