MSLRH | SOC Hunt Feed

Hunt Hypothesis

This detection identifies potential malware or suspicious scripts matching the specific MSLRH signature pattern through YARA analysis on endpoint and cloud workloads. Proactive hunting for this indicator in Azure Sentinel is essential to uncover stealthy adversary activity that may evade standard heuristic alerts due to its low severity classification, ensuring early identification of targeted threats before they escalate.

YARA Rule

rule MSLRH: Packer PEiD
{
      meta:
		author="malware-lu"
        note="Added some checks"
strings:
		$a0 = { 60 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 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 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 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 83 C4 08 2B 04 24 74 04 75 02 EB 02 EB 01 81 83 C4 04 E8 0A 00 00 00 E8 EB 0C 00 00 E8 F6 FF FF FF E8 F2 FF FF FF 83 C4 08 3D FF 0F 00 00 EB 01 68 EB 02 CD 20 EB 01 E8 76 1B EB 01 68 EB 02 CD 20 EB 01 E8 CC 66 B8 FE 00 74 04 75 02 EB 02 EB 01 81 66 E7 64 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 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 83 C4 08 2B 04 24 74 04 75 02 EB 02 EB 01 81 }
        $b = { 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 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 83 C4 08 2B 04 24 74 04 75 02 EB 02 EB 01 81 83 C4 04 E8 0A 00 00 00 E8 EB 0C 00 00 E8 F6 FF FF FF E8 F2 FF FF FF 83 C4 08 3D FF 0F 00 00 EB 01 68 EB 02 CD 20 EB 01 E8 76 1B EB 01 68 EB 02 CD 20 EB 01 E8 CC 66 B8 FE 00 74 04 75 02 EB 02 EB 01 81 66 E7 64 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 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 83 C4 08 2B 04 24 74 04 75 02 EB 02 EB 01 81 83 C4 04 E8 0A 00 00 00 E8 EB 0C 00 00 E8 F6 FF FF FF E8 F2 FF FF FF 83 C4 08 3D FF 0F 00 00 EB 01 68 EB 02 CD 20 EB 01 E8 76 1B EB 01 68 EB 02 CD 20 EB 01 E8 CC 66 B8 FE 00 74 04 75 02 EB 02 EB 01 81 66 E7 64 74 04 75 02 EB 02 EB 01 81 74 04 75 02 EB 02 EB 01 81 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 83 C4 08 2B 04 24 74 04 75 02 EB 02 EB 01 81 83 C4 04 E8 0A 00 00 00 E8 EB 0C 00 00 E8 F6 FF FF FF E8 F2 FF FF FF 83 C4 08 3D FF 0F 00 00 EB 01 68 EB 02 CD 20 EB 01 E8 76 1B EB 01 68 EB 02 CD 20 EB 01 E8 CC 66 B8 FE 00 74 04 75 02 EB 02 EB 01 81 66 E7 64 74 04 75 02 EB 02 EB 01 81 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 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 83 C4 08 2B 04 24 74 04 75 02 EB 02 EB 01 81 83 C4 04 E8 0A 00 00 00 E8 EB 0C 00 00 E8 F6 FF FF FF E8 F2 FF FF FF 83 C4 08 3D FF 0F 00 00 EB 01 68 EB 02 CD 20 EB 01 E8 76 1B EB 01 68 EB 02 CD 20 EB 01 E8 CC 66 B8 FE 00 74 04 75 02 EB 02 EB 01 81 66 E7 64 74 04 75 02 EB 02 EB 01 81 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 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 83 C4 08 2B 04 24 74 04 75 02 EB 02 EB 01 81 83 C4 04 E8 0A 00 00 00 E8 EB 0C 00 00 E8 F6 FF FF FF E8 F2 FF FF FF 83 C4 08 }
        $c = { 60 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 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 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 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 83 C4 08 2B 04 24 74 04 75 02 EB 02 EB 01 81 83 C4 04 E8 0A 00 00 00 E8 EB 0C 00 00 E8 F6 FF FF FF E8 F2 FF FF FF 83 C4 08 3D FF 0F 00 00 EB 01 68 EB 02 CD 20 EB 01 E8 76 1B EB 01 68 EB 02 CD 20 EB 01 E8 CC 66 B8 FE 00 74 04 75 02 EB 02 EB 01 81 66 E7 64 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 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 83 C4 08 }

condition:
		for any of ($*) : ( $ 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 3 string patterns in its detection logic.

Source Rule

False Positive Guidance

Here are 4 specific false positive scenarios for the MSLRH detection rule, including suggested filters and exclusions tailored for an enterprise environment:

Scenario: Scheduled Antivirus Definition Updates
- Context: Enterprise endpoint protection suites (e.g., Microsoft Defender for Endpoint or CrowdStrike Falcon) frequently download and install new signature definitions via scheduled tasks. These processes often spawn child processes that load modules matching the MSLRH YARA signatures, triggering alerts during peak update windows (e.g., 02:00 AM).
- Suggested Filter/Exclusion: Create a time-based exclusion for the specific parent process executing the update.
  - Filter Logic: Exclude if Parent Process Name == "MsMpEng.exe" AND Time is between 01:30 and 04:00 on weekdays.
Scenario: Microsoft Office Add-in Initialization
- Context: When users launch Microsoft Office applications (Word, Excel) with specific third-party add-ins installed (e.g., Adobe Acrobat PDF Editor or Kofax Power PDF), the host process (WINWORD.EXE or EXCEL.EXE) loads COM components that match the MSLRH signature. This is common in environments where document processing tools are mandatory.
- Suggested Filter/Exclusion: Exclude alerts where the parent process belongs to the Microsoft Office suite and the file path contains known add-in directories.
  - Filter Logic: Exclude if Parent Process Name IN ["WINWORD.EXE", "EXCEL.EXE"] AND File Path contains "\Program Files\Microsoft Office\" OR "\AppData\Roaming\Microsoft\Office\".
Scenario: Automated Backup and Archiving Jobs
- Context: Enterprise backup solutions like Veeam or Commvault often utilize compression engines that instantiate temporary modules during the archiving phase.