PEncryptv30

Hunt Hypothesis

This rule detects the presence of encrypted PE files, which adversaries may use to obfuscate malicious payloads or stage tools to evade static analysis. Proactively hunting for these artifacts helps identify hidden implantations or staging activities that could precede execution or lateral movement within the environment.

YARA Rule

rule PEncryptv30
{
      meta:
		author="malware-lu"
strings:
		$a0 = { E8 00 00 00 00 5D 81 ED 05 10 40 00 8D B5 24 10 40 00 8B FE B9 0F 00 00 00 BB [4] AD 33 C3 E2 FA }

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: A developer or operations engineer runs a local build script that uses 7z or WinRAR to compress and encrypt source code archives before pushing them to a private repository. The YARA rule may match the encrypted container header or specific encryption library signatures embedded in the executable or archive file.

  • Filter/Exclusion: Exclude files located in standard development directories (e.g., C:\Users\<user>\Projects\, C:\dev\) or files with extensions like .7z, .rar, and .zip if the rule is designed to detect encrypted executables rather than archives. Additionally, whitelist known build tools like 7z.exe and WinRAR.exe when running from expected developer workstations.

• Scenario: An IT administrator uses BitLocker management utilities or EFS (Encrypting File System) tools to encrypt sensitive configuration files or database backups during a scheduled maintenance window. The encryption process may temporarily create intermediate files or modify file headers in a way that triggers the PEncryptv30 signature.

  • Filter/Exclusion: Exclude processes initiated by bitsadmin.exe, manage-bde.exe, or cipher.exe when running from the C:\Windows\System32\ directory. Also, consider excluding files in backup directories (e.g., C:\Backups\, D:\Archives\) during known maintenance windows.

• Scenario: A third-party application installer (e.g., Adobe Creative Cloud, Microsoft Office, or Java Runtime) uses self-extracting archives or encrypted installers that contain embedded encryption libraries. These installers often reside in C:\Program Files\ or C:\Users\<user>\AppData\Local\Temp\ and may match the YARA pattern due to their encrypted payload structure.

  • Filter/Exclusion: Whitelist