MSLRHv032afakePEBundle20x24xemadicius

Hunt Hypothesis

This detection identifies adversary behavior involving the execution of suspicious fake PE bundles that may indicate early-stage malware staging or obfuscation attempts within the environment. A SOC team should proactively hunt for these artifacts in Azure Sentinel to uncover stealthy threats that evade traditional signature-based defenses and prevent potential lateral movement before escalation occurs.

YARA Rule

rule MSLRHv032afakePEBundle20x24xemadicius
{
      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 83 BD 9C 38 40 00 01 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

Here are 5 specific false positive scenarios for the detection rule MSLRHv032afakePEBundle20x24xemadicius, including suggested filters and exclusions:

• Scenario: Microsoft Office Click-to-Run Updates

  • Context: The background service OfficeClickToRun.exe (Microsoft Office 2016/2019/365) frequently generates temporary PE bundles during the “Update” phase to stage new application components before installation. These bundles often mimic the structural characteristics of the detection rule’s target signature.
  • Filter/Exclusion: Exclude files where the parent process is OfficeClickToRun.exe and the file path contains \Microsoft Office ClickToRun\. Additionally, filter out events occurring within 5 minutes of a known “Update” scheduled task trigger (OfficeBackgroundTaskHandler).

• Scenario: Antivirus Real-Time Scanning of Temporary Archives

  • Context: Endpoint Protection platforms like CrowdStrike Falcon or Microsoft Defender for Endpoint often extract and scan temporary .zip or .cab archives in the %TEMP% directory. During extraction, these tools create transient PE bundles that match the rule’s logic before being immediately deleted by the cleanup routine.
  • Filter/Exclusion: Create a path-based exclusion for files located strictly within C:\Users\<User>\AppData\Local\Temp\ or C:\Windows\Temp. Furthermore, exclude events where the file age is less than 60 seconds and the file size is under 5MB.

• Scenario: Scheduled PowerShell Deployment Scripts

  • Context: Internal IT operations often utilize scheduled tasks (e.g., via SCCM/MECM or Ansible) to deploy software patches using PowerShell.exe. These scripts frequently invoke the `System.Management.Automation