CryptoLockv202EngRyanThian

Hunt Hypothesis

This rule detects the presence of the CryptoLock ransomware variant, specifically targeting the “EngRyanThian” build, which indicates an active encryption or staging phase on a host. Proactively hunting for this signature allows the SOC to identify compromised endpoints early in the kill chain, enabling rapid isolation and containment before the ransomware completes its encryption process and propagates laterally.

YARA Rule

rule CryptoLockv202EngRyanThian
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 60 BE 15 90 40 00 8D BE EB 7F FF FF 57 83 CD FF EB 10 90 90 90 90 90 90 8A 06 46 88 07 47 }
	$a1 = { 60 BE 15 90 40 00 8D BE EB 7F FF FF 57 83 CD FF EB 10 90 90 90 90 90 90 8A 06 46 88 07 47 01 DB 75 07 8B 1E 83 EE FC 11 DB 72 ED B8 01 00 00 00 01 DB 75 07 8B 1E 83 EE FC 11 DB 11 C0 01 DB 73 EF 75 09 8B 1E 83 EE FC 11 DB 73 E4 31 C9 83 E8 03 72 0D C1 E0 }
	$a2 = { 60 BE ?? 90 40 00 8D BE [2] FF FF 57 83 CD FF EB 10 90 90 90 90 90 90 8A 06 46 88 07 47 01 DB 75 07 8B 1E 83 EE FC 11 DB 72 ED B8 01 00 00 00 01 DB 75 07 8B 1E 83 EE FC 11 DB 11 C0 01 DB 73 EF 75 09 8B 1E 83 EE FC 11 DB 73 E4 31 C9 83 E8 03 72 0D C1 E0 }

condition:
		$a0 at pe.entry_point or $a1 at pe.entry_point or $a2 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

• Legitimate Crypto Asset Management Tools: Enterprise environments often deploy specialized software for managing digital assets, such as Bitwarden, 1Password, or KeePassXC. These applications frequently embed cryptographic libraries (e.g., OpenSSL, BouncyCastle) or custom encryption routines for vault storage and key derivation.
  • Filter/Exclusion: Exclude processes where the executable path contains \Bitwarden\, \1Password\, or \KeePass\, or where the parent process is a known browser extension host (e.g., chrome.exe, msedge.exe) launching the crypto helper.
• Database Encryption Key Rotation Tasks: Scheduled maintenance jobs for databases like SQL Server or PostgreSQL may execute external scripts or binaries to rotate Transparent Data Encryption (TDE) keys or re-encrypt data at rest. Tools like DBCC CHECKTABLE or custom PowerShell scripts invoking openssl or gpg can trigger YARA matches if they load specific cryptographic DLLs or execute in-memory encryption routines.
  • Filter/Exclusion: Exclude events where the parent process is sqlservr.exe, postgres.exe, or powershell.exe running from a trusted system path (e.g., C:\Program Files\Microsoft SQL Server\), and the command line contains keywords like rotate, encrypt, or tde.
• CI/CD Pipeline Build Agents: In DevOps environments, build agents (e.g., Jenkins, GitLab Runner, Azure DevOps) execute compilation steps that may invoke cryptographic tools for code signing, artifact encryption, or secret injection. For example, running signtool or openssl dgst during the build phase can load libraries that match the YARA signature.
  • Filter/Exclusion: Exclude processes where the parent process is a known CI/CD agent (