PEnguinCrypt v10

Hunt Hypothesis

This rule detects the presence of PEnguinCrypt ransomware, a known threat actor that encrypts files and appends a specific extension to facilitate ransom demands. Proactively hunting for this signature in Azure Sentinel allows the SOC to identify early-stage infections or dormant payloads before they propagate, reducing the potential impact on Azure-hosted workloads and data stores.

YARA Rule

rule PEnguinCrypt_v10: PEiD
{
    strings:
        $a = { B8 93 ?? ?? 00 55 50 67 64 FF 36 00 00 67 64 89 26 00 00 BD 4B 48 43 42 B8 04 00 00 00 CC 3C 04 75 04 90 90 C3 90 67 64 8F 06 00 00 58 5D BB 00 00 40 00 33 C9 33 C0 }
    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 uses a specialized build tool or custom script that embeds a specific version of the PEnguinCrypt library (or its obfuscated variant) into a CI/CD pipeline artifact for internal testing, where the binary is temporarily stored in a shared network drive or local temp folder.

  • Filter/Exclusion: Exclude files located in known CI/CD working directories (e.g., C:\Jenkins\workspace\, C:\AzureDevOps\agent\_work\) or files with extensions like .tmp, .part, or .bak that are less than 5MB in size, provided they are not in executable directories like C:\Program Files\.

• Scenario: An IT administrator installs a legacy third-party backup or encryption agent (e.g., a specific version of Veeam, Acronis, or a niche endpoint encryption tool) that bundles the PEnguinCrypt v10 library as a dependency for its encryption engine, and the YARA rule scans the installed service DLLs or executables during a routine integrity check.

  • Filter/Exclusion: Exclude known vendor directories such as C:\Program Files\Veeam\, C:\Program Files\Acronis\, or C:\Program Files (x86)\[VendorName]\ and specifically whitelist known good hashes or file paths for these vendor binaries if they match the YARA signature.

• Scenario: A security team runs a sandboxed analysis or a “canary” test where they intentionally deploy a benign copy of the PEnguinCrypt v10 sample to a non-production test VM or a dedicated security lab host to verify detection coverage, and the rule triggers on the test host.

  • Filter/Exclusion: Exclude hosts tagged in the CMDB or asset inventory as “Test,” “Lab,” or “Sandbox