BeRoEXEPackerv100LZMABeRoFarbrausch

Hunt Hypothesis

This detection identifies the presence of Farbrausch-packed executables, which adversaries frequently employ to obfuscate malicious payloads and evade signature-based analysis within Azure Sentinel. Proactive hunting for this specific packing technique is essential to uncover stealthy threats that may bypass standard antivirus solutions by leveraging low-severity alerts as an early indicator of potential fileless or packed malware activity.

YARA Rule

rule BeRoEXEPackerv100LZMABeRoFarbrausch
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 60 68 [4] 68 [4] 68 [4] E8 [4] BE [4] B9 04 00 00 00 8B F9 81 FE [4] 7F 10 AC 47 04 18 2C 02 73 F0 29 3E 03 F1 03 F9 EB E8 }

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

Here are 5 specific false positive scenarios for the BeRoEXEPackerv100LZMABeRoFarbrausch detection rule, along with recommended filters and exclusions:

• Scenario: Enterprise Antivirus Scanner Activity

  • Context: The YARA rule likely detects the “Farbrausch” packing signature often used in legitimate security tools. In an enterprise environment, scheduled scans by Microsoft Defender for Endpoint or Symantec Endpoint Protection frequently unpack and analyze executable components that trigger this specific packing signature during routine background scans.
  • Filter/Exclusion: Create a process exclusion based on the host name of the scanner service (e.g., MsMpEng.exe, Rtvscan64.exe) or exclude files located within the vendor’s installation directory (e.g., C:\Program Files\Microsoft Defender\).

• Scenario: Software Deployment via SCCM/Intune

  • Context: During mass software deployments, tools like Microsoft Endpoint Configuration Manager (SCCM) or Microsoft Intune often utilize installers wrapped in the Farbrausch packer to ensure compatibility across diverse OS builds. When these agents push updates or new applications to workstations, the installer executable triggers the rule upon extraction.
  • Filter/Exclusion: Exclude processes spawned by deployment services such as ccmsetup.exe (SCCM) or IntuneManagementExtension.exe. Additionally, filter out events where the file path contains standard deployment staging folders like C:\Windows\CCMCache\ or C:\ProgramData\Microsoft\Intune Management Extension.

• Scenario: Scheduled Backup and Archiving Jobs

  • Context: Enterprise backup solutions often compress and package large datasets before transmission. Tools like Veeam Backup & Replication or Acronis Cyber Protect may utilize the Far