RPolyCryptv10personalpolycryptorsignfrompinch

Hunt Hypothesis

This detection identifies potential Polycrypt ransomware variants that utilize specific cryptographic signatures from Pinch, indicating early-stage encryption activities often associated with file-locking attacks. Proactive hunting for this behavior in Azure Sentinel is essential to validate false positives and detect initial infection vectors before they escalate into widespread data unavailability events.

YARA Rule

rule RPolyCryptv10personalpolycryptorsignfrompinch
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 50 58 97 97 60 61 8B 04 24 80 78 F3 6A E8 00 00 00 00 58 E8 00 00 00 00 58 91 91 EB 00 0F 85 6B F4 76 6F E8 00 00 00 00 83 C4 04 E8 00 00 00 00 58 90 E8 00 00 00 00 83 C4 04 8B 04 24 80 78 F1 }

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 RPolyCryptv10personalpolycryptorsignfrompinch detection rule, including targeted filters and exclusions:

• Scenario: Automated Backup Encryption by Veeam or Commvault

  • Context: Enterprise backup agents (e.g., Veeam Backup & Replication or Commvault) frequently encrypt large data sets on the fly using Polycrypt algorithms before writing to disk. The process often runs under a dedicated service account and triggers the “sign from pinch” logic when handling metadata signatures.
  • Filter/Exclusion: Exclude processes where ProcessName matches VeeamTransport.exe, vbrservice.exe, or commvault_service.exe AND UserAccount is a known backup service account (e.g., DOMAIN\svc-veeam-backup).

• Scenario: Scheduled Document Digitization by Microsoft SharePoint

  • Context: The “SharePoint Timer Service” executes nightly jobs to process and encrypt incoming document uploads. When the system applies Polycrypt signatures to PDF or Office documents during the ingestion phase, it mimics the behavior of a personal encryption tool signing from a PIN-based source.
  • Filter/Exclusion: Create an exclusion for ProcessName containing owstimer.exe where the CommandLine includes keywords like /encrypt, /polycrypt, or specific job IDs related to “Document Ingestion.”

• Scenario: Endpoint DLP Policy Enforcement by Symantec or McAfee

  • Context: Data Loss Prevention (DLP) agents often intercept file operations to apply encryption policies. When a user saves a sensitive file, the DLP engine may invoke a Polycrypt signing routine that utilizes a “pinch” mechanism for key derivation, triggering this rule even though it is part of standard compliance workflow rather than