MSLRHv032afakeEXE32Pack13xemadicius

Hunt Hypothesis

This hunt detects the execution of a potentially malicious 32-bit executable exhibiting characteristics consistent with the XEMADICIUS malware family, which often utilizes packing techniques to evade standard signature-based detection. A proactive search in Azure Sentinel is essential because low-severity alerts for such packed executables may be overlooked by automated triage, yet they frequently represent early-stage adversary activity that could escalate into a significant compromise if not investigated immediately.

YARA Rule

rule MSLRHv032afakeEXE32Pack13xemadicius
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 3B C0 74 02 81 83 55 3B C0 74 02 81 83 53 3B C9 74 01 BC 56 3B D2 74 02 81 85 57 E8 00 00 00 00 3B DB 74 01 90 83 C4 14 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 4 specific false positive scenarios for the MSLRHv032afakeEXE32Pack13xemadicius detection rule, which targets suspicious 32-bit executable packing and potential “fake” EXE structures often associated with malware:

• Scenario: Legitimate Software Updates via Microsoft Update Standalone Packages

  • Context: When the Microsoft Update Service (or a third-party patch management tool like SCCM/ConfigMgr) deploys standalone .msi or .exe installers for critical patches (e.g., Office 365 updates, .NET Framework patches). These packages often utilize complex packing algorithms that mimic the structural characteristics of the “fake EXE” signature.
  • Filter/Exclusion: Exclude processes where ImageFileName matches known Microsoft update executables and the parent process is WindowsUpdate.exe or ccmsetup.exe.
    • Example Filter: ProcessName IN ("MicrosoftEdgeUpdate.exe", "OfficeClickToRun.exe") AND ParentProcessName IN ("TrustedInstaller.exe", "ccmexec.exe").

• Scenario: Scheduled Antivirus Definition Updates

  • Context: Major Endpoint Detection and Response (EDR) or Antivirus solutions (e.g., CrowdStrike Falcon, SentinelOne, Microsoft Defender) frequently download and unpack definition updates in the background. These update agents often generate temporary 32-bit executables with packed headers that trigger this YARA rule during the nightly maintenance window.
  • Filter/Exclusion: Create an exclusion for processes running under the System account or specific service accounts (e.g., NT SERVICE\DefenderSvc) where the file path resides in a trusted vendor directory.
    • Example Filter: `FilePath CONTAINS “\Program Files\CrowdStrike” OR FilePath CONTAINS ”\