WarningmaybeSimbyOZpolycryptorby3xpl01tver2xx250320072200

Hunt Hypothesis

This YARA rule targets a specific variant of the SimbyOZ poly cryptor, indicating the presence of a low-severity ransomware or file encryption payload that may be used for initial compromise or lateral movement. Proactively hunting for this signature in Azure Sentinel allows the SOC to identify dormant or early-stage infections on endpoints before the cryptor fully executes and locks user data, reducing the potential impact of a low-fidelity threat.

YARA Rule

rule WarningmaybeSimbyOZpolycryptorby3xpl01tver2xx250320072200
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 57 57 8D 7C 24 04 50 B8 00 D0 17 13 AB 58 5F C3 00 00 }

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 DevOps engineer uses a legitimate open-source cryptographic utility (such as openssl or a custom Go/Rust-based encryption tool) to encrypt large data files or backup archives in a staging or development environment. The binary may contain specific string patterns or structural elements that loosely match the “polycryptor” heuristic, triggering the YARA rule.

  • Filter/Exclusion: Exclude processes where the parent process is a known development tool (e.g., code.exe, idea64.exe, python.exe) or where the file path resides in standard development directories (e.g., C:\dev\, C:\projects\, C:\Users\<User>\.vscode\). Additionally, exclude if the process is launched by a known IDE or build agent (e.g., jenkins.exe, azure-pipelines-agent.exe).

• Scenario: An IT administrator runs a scheduled PowerShell script or a custom utility to encrypt sensitive configuration files or database backups using a proprietary or third-party encryption wrapper. The wrapper might be a small, statically linked binary that shares similar entropy or string characteristics with the cryptor family, leading to a false positive.

  • Filter/Exclusion: Exclude processes where the command line arguments contain known encryption keywords (e.g., encrypt, aes, cipher) and the parent process is a scheduled task runner (e.g., svchost.exe with TasksSched service, or powershell.exe invoked by Task Scheduler). Also, exclude if the file is located in a trusted admin tools directory (e.g., C:\AdminTools\, C:\Scripts\).

• Scenario: A security team or application owner runs a legitimate file integrity monitoring (FIM) or hashing tool (like sha256sum, md5sum, or a custom C#/.NET hashing