SimbiOZ PolyCryptor vxx Extranger additional

Hunt Hypothesis

This hypothesis targets the presence of SimbiOZ PolyCryptor vxx Extranger, a ransomware variant that encrypts files to deny access to critical data. Proactively hunting for this specific YARA signature allows the SOC team to identify early-stage infections or dormant payloads before the encryption process completes, minimizing potential business impact in the Azure Sentinel environment.

YARA Rule

rule SimbiOZ_PolyCryptor_vxx_Extranger_additional: PEiD
{
    strings:
        $a = { 55 60 E8 00 00 00 00 5D 81 ED ?? ?? ?? ?? 8D 85 ?? ?? ?? ?? 68 ?? ?? ?? ?? 50 E8 }
    condition:
        $a 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 runs a local build script using polycrypt or a similar multi-encryption wrapper to test data resilience before deploying a new application version. The YARA rule may match the specific byte patterns or string signatures of the “vxx” variant if the tool is statically linked or if the encryption key structure matches the rule’s heuristic.

  • Filter/Exclusion: Exclude processes where the parent process is python.exe, node.exe, or bash.exe and the working directory contains build/, test/, or dev/ subdirectories. Additionally, exclude file paths matching C:\Users\<username>\Projects\* or C:\dev\builds\*.

• Scenario: An IT administrator uses a specialized data sanitization tool (e.g., a custom wrapper around gpg or openssl with a specific poly-crypt mode) to securely wipe sensitive logs from a decommissioned server. The tool’s binary or temporary output files may exhibit the “Extranger” signature pattern if the encryption algorithm is implemented in a non-standard way.

  • Filter/Exclusion: Exclude processes named sanitizer.exe, wipe_tool.exe, or log_cleaner.ps1. Also, exclude file paths under C:\Admin\Tools\ or C:\Scripts\maintenance\.

• Scenario: A security team performs a tabletop exercise or a controlled ransomware simulation in a non-production environment (e.g., a staging VM) to validate detection capabilities. The simulation uses a modified version of the SimbiOZ PolyCryptor vxx “Extranger” variant to mimic real-world behavior, triggering the rule as intended.

  • Filter/Exclusion: Exclude hosts tagged with Environment=Staging or Tag=RedTeam in the CMDB or asset inventory. Additionally