MSLRHv032afakePEBundle023xemadicius

Hunt Hypothesis

This detection identifies adversary behavior involving the execution of suspicious PE bundles that mimic legitimate software structures to evade static analysis and conceal malicious payloads within the Azure Sentinel environment. The SOC team should proactively hunt for this activity because these fake bundles often serve as initial footholds for advanced threats, allowing attackers to establish persistence before triggering higher-severity alerts or initiating lateral movement.

YARA Rule

rule MSLRHv032afakePEBundle023xemadicius
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 9C 60 E8 02 00 00 00 33 C0 8B C4 83 C0 04 93 8B E3 8B 5B FC 81 EB 07 30 40 00 87 DD 61 9D EB 05 E8 EB 04 40 00 EB FA E8 0A 00 00 00 E8 EB 0C 00 00 E8 F6 FF FF FF E8 F2 FF FF FF 83 C4 08 74 04 75 02 EB 02 EB 01 81 50 E8 02 00 00 00 29 5A 58 6B C0 03 E8 02 00 00 00 29 5A 83 C4 04 58 74 04 75 02 EB 02 EB 01 81 0F 31 50 0F 31 E8 0A 00 00 00 E8 EB 0C 00 00 E8 F6 FF FF FF E8 F2 FF FF FF }

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: Antivirus Engine Signature Updates

  • Context: The enterprise endpoint protection suite (e.g., CrowdStrike Falcon or Microsoft Defender for Endpoint) performs automatic signature definition updates. These updates often involve downloading and unpacking a bundle of PE (Portable Executable) files that mimic the structure detected by this YARA rule, specifically containing embedded resources resembling fake bundles.
  • Filter/Exclusion: Create an exclusion based on the process image path for the AV updater service (e.g., C:\Program Files\CrowdStrike\csfalcon.exe or C:\ProgramData\Microsoft\Windows Defender\platform\4.18.xxxxxx\mpcmdrun.exe) and exclude events where the parent process is the Windows Update Service (usocoreworker.exe).

• Scenario: Scheduled Software Deployment via SCCM/Intune

  • Context: During a nightly maintenance window, System Center Configuration Manager (SCCM) or Microsoft Intune pushes application packages to endpoints. The deployment agent extracts a compressed bundle containing multiple executables and manifests that match the “fake PE Bundle” signature logic before installing them into the C:\Windows\CCMCache directory.
  • Filter/Exclusion: Exclude alerts where the file path resides within the application cache directories (e.g., paths starting with C:\ProgramData\Microsoft\IntuneManagementExtension\ or C:\Windows\CCMCache\) and the process name is ccmsetup.exe, intunemanager.exe, or TaskSchedulerService.

• Scenario: Enterprise Backup Agent Activity

  • Context: The Veeam Backup & Replication agent (or similar tools like Commvault) runs a scheduled job to create incremental backups. During the indexing phase, the agent generates temporary PE bundles and manifests in the backup working directory (`C:\Program Files\V