BeRoEXEPackerv100DLLLZBRRBeRoFarbrausch

Hunt Hypothesis

This detection identifies potential malware activity by leveraging a specific YARA signature to scan for the presence of the BeRoEXE packer or Farbrausch-related artifacts within executable files and DLLs. The SOC team should proactively hunt for these indicators in Azure Sentinel to uncover stealthy, packed executables that may evade standard signature-based defenses and facilitate early-stage threat identification before lateral movement occurs.

YARA Rule

rule BeRoEXEPackerv100DLLLZBRRBeRoFarbrausch
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 83 7C 24 08 01 0F 85 [4] 60 BE [4] BF [4] FC B2 80 33 DB A4 B3 02 E8 [4] 73 F6 33 C9 E8 [4] 73 1C 33 C0 E8 [4] 73 23 B3 02 41 B0 10 }

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 4 specific false positive scenarios for the BeRoEXEPackerv100DLLLZBRRBeRoFarbrausch detection rule, including suggested filters and exclusions:

• Scenario: Microsoft Office Click-to-Run Updates

  • Context: The YARA rule likely detects packed DLLs or specific header structures common in modern installers. When the Microsoft Office Click-to-Run Service (OfficeClickToRun.exe) executes background updates, it frequently unpacks and loads temporary DLLs that match the “Farbrausch” signature pattern.
  • Filter/Exclusion: Exclude the process path C:\Program Files\Microsoft Office\root\Office16\* or specifically filter for the parent process OfficeClickToRun.exe. Additionally, exclude file paths containing \AppData\Local\Temp\Microsoft Office Click-to-Run\*.dll.

• Scenario: Scheduled Antivirus Engine Scans (CrowdStrike/Dragon)

  • Context: During scheduled morning scans, enterprise EDR agents like CrowdStrike Falcon or Palo Alto Cortex XDR often load proprietary scanning engines that utilize similar packing mechanisms. The rule may trigger when the agent’s core service (C:\Program Files\CrowdStrike\fs_qr.exe or XDRService) injects a packed DLL into memory for real-time analysis.
  • Filter/Exclusion: Create an exclusion based on the parent process name FalconSensor.exe (CrowdStrike) or PaloAltoNetworksAgent.exe. Alternatively, exclude file hashes that match known good signatures of these specific EDR components in your whitelist database.

• Scenario: Windows Defender Real-Time Protection Updates

  • Context: The Windows Update service (wuauserv) often triggers the download and installation of new definition packs for