SimbiOZPolyCryptorvxxExtranger

Hunt Hypothesis

This hypothesis targets the execution of the SimbiOZ PolyCryptor, a known ransomware strain, by identifying its unique code patterns to detect early-stage encryption activities before full payload deployment. Proactively hunting for this signature in Azure Sentinel allows the SOC to identify compromised workloads or containers that may have been infected via supply chain attacks or lateral movement, enabling rapid isolation before the encryption process propagates across the environment.

YARA Rule

rule SimbiOZPolyCryptorvxxExtranger
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 55 60 E8 00 00 00 00 5D 81 ED [4] 8D 85 [4] 68 [4] 50 E8 }

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 is performing a manual backup or migration of a legacy application using a custom script that embeds a specific version of the SimbiOZPolyCryptor (e.g., for data-at-rest encryption in a test environment). The YARA rule matches the binary because it contains the expected string signatures and structural patterns of the cryptor, even though it is being used intentionally for encryption rather than malicious ransomware encryption.

  • Filter/Exclusion: Exclude processes where the parent process is a known scripting interpreter (e.g., powershell.exe, python.exe, node.exe) and the target file path resides in a designated “Dev-Backup” or “Legacy-Migration” directory (e.g., C:\Projects\LegacyApp\Backups\). Additionally, exclude if the process command line contains specific flags like --encrypt or --backup.

• Scenario: An IT administrator is testing a new endpoint protection solution or a custom encryption tool in a non-production lab environment. They deploy a sample or a modified build of the SimbiOZPolyCryptor to verify how the EDR responds to known cryptor signatures. The detection triggers because the binary is intentionally placed on the endpoint and executed to simulate an attack.

  • Filter/Exclusion: Exclude hosts tagged with the AD group or tag Lab-Environment or Test-Bench. Alternatively, exclude if the user account belongs to the IT-Lab-Admins group and the process execution time falls within the defined “Testing Window” (e.g., 10:00 AM – 2:00 PM on weekdays).

• Scenario: A software vendor’s installer or update package includes a helper utility based on the SimbiOZPolyCryptor to encrypt configuration files or license keys during installation. This utility is a small, standalone binary that matches the YARA