BeRoEXEPackerv100LZBRRBeRoFarbrausch

Hunt Hypothesis

This detection identifies the presence of the Farbrausch executable packer, which adversaries frequently employ to obfuscate malicious binaries and evade signature-based security controls. Proactively hunting for this specific packing technique in Azure Sentinel allows the SOC team to uncover stealthy threats that may bypass initial scans by analyzing file entropy and behavioral anomalies associated with packed executables.

YARA Rule

rule BeRoEXEPackerv100LZBRRBeRoFarbrausch
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 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 3-5 specific false positive scenarios for the BeRoEXEPackerv100LZBRRBeRoFarbrausch detection rule, tailored for an enterprise environment:

• Scenario: Automated Deployment of Microsoft Office Updates via SCCM/Intune

  • Context: During scheduled maintenance windows, System Center Configuration Manager (SCCM) or Microsoft Intune pushes cumulative updates to the “Office 2016/2019 Click-to-Run” service. The update installer (setup.exe or ospp.vbs) often utilizes a packed executable structure that matches the “Farbrausch” signature logic, triggering the rule when the agent scans the temporary download folder.
  • Suggested Filter: Exclude processes where the parent process name is ccmexec.exe (SCCM) or Microsoft.IntuneManagementAgent.exe, and the file path contains \Microsoft Office\OfficeUpdates\.

• Scenario: Execution of Endpoint Protection Signature Updates by CrowdStrike Falcon

  • Context: The CrowdStrike Falcon sensor (C-Service.exe) periodically downloads and unpacks new detection signatures. The signature update module often employs a custom packing mechanism for the binary payload that mimics the rule’s heuristic, causing alerts during the nightly update cycle (typically 02:00 – 04:00).
  • Suggested Filter: Create an exclusion for files located in C:\ProgramData\CrowdStrike\ where the process name is csfalcon.exe or C-Service.exe, specifically when the file extension is .cab or .exe and the file age is less than 24 hours.

• Scenario: Scheduled Backup Job Execution by Veeam Agent for Microsoft Windows

  • Context: When Veeam performs a scheduled “Full” backup of system state, it extracts temporary