PEBundlev20b5v23

Hunt Hypothesis

This detection identifies potential process injection or execution anomalies by monitoring for specific PE Bundle signatures that may indicate an adversary attempting to obfuscate malicious payloads within legitimate processes. Proactive hunting in Azure Sentinel is essential to uncover stealthy lateral movement or command-and-control activities that evade standard signature-based defenses, ensuring early identification of low-severity threats before they escalate.

YARA Rule

rule PEBundlev20b5v23
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 9C 60 E8 02 [3] 33 C0 8B C4 83 C0 04 93 8B E3 8B 5B FC 81 EB [2] 40 ?? 87 DD 01 AD [4] 01 AD }

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 PEBundlev20b5v23 detection rule in an enterprise environment:

• Scenario: Legitimate deployment of Microsoft Office updates via Configuration Manager (SCCM/MECM) or Intune. The YARA rule may flag the OfficeC2RClient.exe process when it executes bundled update packages containing multiple DLLs and EXEs, triggering a match on the PEBundle signature structure.

  • Suggested Filter: Exclude processes with the executable path matching C:\Program Files\Microsoft Office*\root\office16\* or specifically targeting OfficeC2RClient.exe where the parent process is ccmexec.exe (SCCM) or IntuneManagementExtension.exe.

• Scenario: Execution of scheduled antivirus definition updates by CrowdStrike Falcon or Microsoft Defender. These agents often utilize bundled payloads to distribute new signature databases, which can mimic the structural characteristics detected by PEBundlev20b5v23 during the extraction phase.

  • Suggested Filter: Create an exclusion for processes named Cns.exe (CrowdStrike) or MsMpEng.exe (Defender) running under the context of the “System” user, specifically when the command line arguments contain keywords like “update”, “scan”, or “definition”.

• Scenario: Automated software installation tasks performed by enterprise deployment tools such as Ansible Tower or Puppet. When these agents push application bundles to endpoints, they often extract compressed archives containing executable payloads that match the PEBundle heuristic.

  • Suggested Filter: Exclude events where the parent process is ansible-runner.exe, puppet-agent.exe, or msiexec.exe (when invoked by a scheduled task), and the file extension of the triggered object is .exe located within the C:\ProgramData\ directory