PEnguinCryptv10

Hunt Hypothesis

This detection identifies potential early-stage file encryption activities associated with the PEnguin ransomware variant by leveraging specific YARA signatures to monitor for suspicious process behaviors. Proactive hunting in Azure Sentinel is essential to uncover stealthy initial infection vectors before they escalate into full-scale data exfiltration or widespread system lockouts, ensuring rapid containment of low-severity threats that may otherwise go unnoticed.

YARA Rule

rule PEnguinCryptv10
{
      meta:
		author="malware-lu"
strings:
		$a0 = { B8 93 [2] 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:
		$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

Here are 3-5 specific false positive scenarios for the PEnguinCryptv10 detection rule, including suggested filters and exclusions tailored for an enterprise environment:

• Scenario: Automated Backup Encryption by Veeam or Commvault

  • Context: Enterprise backup agents (e.g., Veeam Backup & Replication, Commvault) frequently encrypt large data sets or perform on-the-fly encryption during backup jobs. These processes often utilize cryptographic libraries that mimic the behavior of ransomware families like PEnguin, triggering alerts when they scan and lock temporary files in network shares or local storage.
  • Suggested Filter/Exclusion: Create a process exclusion for the specific backup service executables (e.g., Veeam.Backup.Service.exe, commvault_agent.exe) running under the SYSTEM or dedicated backup service accounts (DOMAIN\BackupSvc). Exclude file paths within known backup directories (e.g., C:\ProgramData\Veeam\Backup\...).

• Scenario: Scheduled Antivirus Deep Scan by Microsoft Defender or CrowdStrike

  • Context: During scheduled deep scans, endpoint protection agents often re-encrypt or quarantine files that match specific heuristic patterns. The YARA rule may misinterpret the high volume of file I/O and cryptographic hash operations performed by the AV engine during a full system scan as an active encryption event characteristic of PEnguinCryptv10.
  • Suggested Filter/Exclusion: Implement a time-based exclusion window for the detection logic (e.g., exclude alerts generated between 02:00 and 04:00 UTC when nightly scans occur). Alternatively, add an exclusion for processes named MsMpEng.exe or csagent.exe specifically when they are performing “Scan” operations rather than real-time protection.

• **Scenario: Document Management System (DMS) Indexing by