PIRITv15

Hunt Hypothesis

This hunt hypothesis targets adversary behavior where malicious actors deploy variants of the PIRIT ransomware family to encrypt critical data and demand ransoms. A SOC team should proactively hunt for these indicators in Azure Sentinel because early detection of low-severity PIRIT signatures allows for rapid containment before the ransomware executes its full encryption payload, minimizing potential operational disruption.

YARA Rule

rule PIRITv15
{
      meta:
		author="malware-lu"
strings:
		$a0 = { B4 4D CD 21 E8 [2] FD E8 [2] B4 51 CD 21 }

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 4 specific false positive scenarios for the PIRITv15 detection rule, including targeted filters and exclusions:

• Scenario: Enterprise Backup Agents Performing File Encryption

  • Context: Legitimate backup solutions like Veeam Backup & Replication or Rubrik often encrypt large datasets during scheduled jobs (e.g., nightly at 02:00 AM). The PIRITv15 rule may misinterpret the rapid, sequential encryption of database files (.vmdk, .vhd) by these agents as ransomware activity.
  • Filter/Exclusion: Exclude processes running under the Veeam.Backup.Service.exe or rubrik-agent service accounts from the detection scope. Additionally, add a filter to ignore file modification events where the source process is located in the C:\Program Files\Veeam\ directory path.

• Scenario: Scheduled Antivirus Definition Updates and Scans

  • Context: During off-hours, tools like Microsoft Defender for Endpoint or Symantec Endpoint Protection perform full system scans and update their definition databases. These operations involve heavy file I/O and temporary locking of files, which can mimic the “file locking” behavior characteristic of PIRIT ransomware variants.
  • Filter/Exclusion: Create a whitelist for process names MsMpEng.exe (Defender) and Symantec Endpoint Protection Client. Configure the rule to suppress alerts when the file extension being modified is .dat, .cab, or .msi, which are common for definition updates rather than user documents.

• Scenario: Automated Deployment Scripts via Configuration Management

  • Context: IT operations teams use tools like Ansible, Puppet, or Microsoft SCCM (Configuration Manager) to push configuration changes or software patches. These agents often execute