BeRoEXEPackerv100DLLLZBRSBeRoFarbrausch

Hunt Hypothesis

This hypothesis targets the presence of executable files packed with the LZBRS algorithm, a technique often used by adversaries to compress payloads and evade static analysis during initial access or lateral movement. Proactively hunting for these specific packed binaries in Azure Sentinel helps identify low-severity anomalies that may indicate stealthy malware staging or obfuscated tooling before they trigger more complex behavioral detections.

YARA Rule

rule BeRoEXEPackerv100DLLLZBRSBeRoFarbrausch
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 83 7C 24 08 01 0F 85 [4] 60 BE [4] BF [4] FC AD 8D 1C 07 B0 80 3B FB 73 3B E8 [4] 72 03 A4 EB F2 E8 [4] 8D 51 FF E8 [4] 56 8B F7 2B F2 F3 A4 5E EB DB 02 C0 75 03 AC 12 C0 C3 33 }

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: Execution of the UPX (Ultimate Packer for eXecutables) utility by a DevOps engineer or CI/CD pipeline to compress release binaries for distribution.
  • Filter/Exclusion: Exclude processes where the parent process is a known build tool (e.g., msbuild.exe, dotnet.exe, python.exe running a build script) or where the file path resides in a dedicated build artifact directory (e.g., C:\Builds\, D:\Artifacts\).
• Scenario: Execution of 7-Zip (7z.exe) or WinRAR (WinRAR.exe) by an administrator to compress a large log archive or backup set, where the compression algorithm (LZMA/BZIP2) matches the “LZBRS” heuristic in the rule name.
  • Filter/Exclusion: Exclude processes initiated by explorer.exe (user-driven compression) or specific administrative scripts (e.g., backup.ps1, compress_logs.bat) that explicitly invoke compression tools.
• Scenario: Execution of Git for Windows (git.exe) or Visual Studio Code (code.exe) when performing repository operations that involve packing or compressing objects, particularly if the rule triggers on the internal DLLs used for compression.
  • Filter/Exclusion: Exclude processes where the parent is git.exe, code.exe, or node.exe (common in VS Code extensions) and the working directory is within a known source code repository path (e.g., C:\Src\, C:\Projects\).
• Scenario: Execution of Java (java.exe) or JVM-based applications (e.g., Tomcat, Spring Boot) that use native compression libraries (like ZLIB or BZIP2) for data processing or logging,