PEEncrypt10Liwuyue

Hunt Hypothesis

This YARA rule targets executable files exhibiting specific encryption or packing characteristics associated with the “PEEncrypt10Liwuyue” signature, which may indicate the presence of obfuscated malware or trojans designed to evade static analysis. Proactively hunting for these artifacts in Azure Sentinel helps identify low-severity, potentially stealthy threats that could serve as initial access vectors or persistence mechanisms before they escalate in severity.

YARA Rule

rule PEEncrypt10Liwuyue
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 55 8B EC 83 C4 D0 53 56 57 8D 75 FC 8B 44 24 30 25 00 00 FF FF 81 38 4D 5A 90 00 74 07 2D 00 10 00 00 EB F1 89 45 FC E8 C8 FF FF FF 2D 0F 05 00 00 89 45 F4 8B 06 8B 40 3C 03 06 8B 40 78 03 06 8B C8 8B 51 20 03 16 8B 59 24 03 1E 89 5D F0 8B 59 1C 03 1E 89 5D EC 8B 41 18 8B C8 49 85 C9 72 5A 41 33 C0 8B D8 C1 E3 02 03 DA 8B 3B 03 3E 81 3F 47 65 74 50 75 40 8B DF 83 C3 04 81 3B 72 6F 63 41 75 33 8B DF 83 C3 08 81 3B 64 64 72 65 75 26 83 C7 0C 66 81 3F 73 73 }

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: Automated Patching via SCCM or Intune

  • Description: When System Center Configuration Manager (SCCM) or Microsoft Intune applies Windows Updates or software deployments, the underlying WindowsUpdate service or T-Client process may temporarily encrypt or transform PE headers of updated binaries (e.g., w32time.dll, msvcr120.dll) to verify integrity or apply patches, triggering the PEEncrypt10Liwuyue heuristic.
  • Filter/Exclusion: Exclude alerts where the parent process is ccmexec.exe (SCCM) or MsMpEng.exe (if integrated with Defender) and the file path resides in C:\Windows\WinSxS\ or C:\ProgramData\Microsoft\Windows\WER\.

• Scenario: Antivirus Real-Time Scanning with Encryption Heuristics

  • Description: Enterprise AV solutions like CrowdStrike Falcon or Microsoft Defender for Endpoint may use in-memory encryption or temporary file encryption during real-time scanning to prevent interference. If the YARA rule scans files while they are in a transient encrypted state (e.g., in C:\ProgramData\Microsoft\Windows Defender\Scans\ or C:\Temp\), it may misinterpret the encrypted PE structure as malicious.
  • Filter/Exclusion: Exclude files located in standard AV cache directories (C:\ProgramData\Microsoft\Windows Defender\, C:\Program Files\CrowdStrike\) or files with a .tmp extension that are less than 5 minutes old.

• Scenario: .NET Assembly Compilation and Obfuscation

  • Description: During CI/CD pipelines or developer builds, tools like dotnet build or msbuild.exe may generate intermediate assemblies that use standard obfuscation or compression