PAVCryptorPawningAntiVirusCryptormasha dev

Hunt Hypothesis

This detection identifies adversary behavior where attackers employ anti-vision evasion tactics to mask ransomware or cryptolocker activities within the environment. A SOC team should proactively hunt for this signature in Azure Sentinel to uncover stealthy encryption campaigns that traditional security controls might overlook due to their low-severity classification and specialized YARA logic.

YARA Rule

rule PAVCryptorPawningAntiVirusCryptormasha_dev
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 53 56 57 55 BB 2C [2] 70 BE 00 30 00 70 BF 20 [2] 70 80 7B 28 00 75 16 83 3F 00 74 11 8B 17 89 D0 33 D2 89 17 8B E8 FF D5 83 3F 00 75 EF 83 3D 04 30 00 70 00 74 06 FF 15 54 30 00 70 80 7B 28 02 75 0A 83 3E 00 75 05 33 C0 89 43 0C FF 15 1C 30 00 70 80 7B 28 01 76 05 83 3E 00 74 22 8B 43 10 85 C0 74 1B FF 15 14 30 00 70 8B 53 10 8B 42 10 3B 42 04 74 0A 85 C0 74 06 50 E8 8F FA FF FF FF 15 20 30 00 70 80 7B 28 01 75 03 FF 53 24 80 7B 28 00 74 05 E8 35 FF FF FF 83 3B 00 75 17 83 3D 10 [2] 70 00 74 06 FF 15 10 [2] 70 8B 06 50 E8 A9 FA FF FF 8B 03 56 8B F0 8B FB B9 0B 00 00 00 F3 A5 5E E9 73 FF FF FF 5D 5F 5E 5B C3 A3 00 30 00 70 E8 26 FF FF FF C3 90 8F 05 04 30 00 70 E9 E9 FF FF FF C3 }

condition:
		$a0
}

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 5 specific false positive scenarios for the PAVCryptorPawningAntiVirusCryptormasha_dev detection rule, including suggested filters and exclusions:

• Endpoint Antivirus Real-Time Scanning on Large Archives

  • Scenario: The YARA rule flags the behavior of legitimate antivirus engines (e.g., CrowdStrike Falcon, Microsoft Defender for Endpoint, or Symantec Endpoint Protection) when they perform real-time scanning on large compressed archives (.zip, .7z) containing executable payloads. The “masha” component often mimics encryption behaviors that trigger the rule during the decompression and inspection phase.
  • Filter/Exclusion: Exclude processes where ImageName matches known AV service binaries (e.g., C:\Program Files\CrowdStrike\fsqa.exe, C:\Windows\System32\mpcmdrun.exe) AND the parent process is a scheduled task or the AV engine itself.

• Scheduled Backup and Encryption Jobs

  • Scenario: Enterprise backup solutions like Veeam Backup & Replication, Rubrik, or Acronis Cyber Protect execute nightly jobs that encrypt data blocks before writing them to storage. The rule may misinterpret the encryption routine of these tools as a cryptor pawning event, specifically when the backup agent spawns child processes to handle chunked file processing.
  • Filter/Exclusion: Create an exclusion for process trees where the root parent is a recognized backup service (e.g., Veeam.Backup.Service.exe, rubrik-agent.exe) and the file extension being processed is .vbk, .rbk, or .acronis.

• Software Deployment via Microsoft Endpoint Configuration Manager (MECM/SCCM)

  • Scenario: During application deployments, Microsoft SCCM or Intune Management Extension utilizes temporary