PENightMare2Beta

Hunt Hypothesis

This hunt hypothesis targets the PENightMare2Beta malware variant to identify early-stage file encryption and persistence activities that may precede a ransomware attack. Proactively hunting for these indicators within Azure Sentinel allows the SOC team to detect low-severity anomalies before they escalate into critical incidents, ensuring timely containment of potential threats.

YARA Rule

rule PENightMare2Beta
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 60 E9 [4] EF 40 03 A7 07 8F 07 1C 37 5D 43 A7 04 B9 2C 3A }

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 5 specific false positive scenarios for the PENightMare2Beta detection rule, along with recommended filters and exclusions:

• Enterprise Backup Agent File Encryption

  • Scenario: The Veeam Backup & Replication service performs nightly incremental backups, encrypting large database files (e.g., .vmdk or .bak) using AES-256. This mass file modification mimics the ransomware encryption behavior targeted by PENightMare2Beta.
  • Filter/Exclusion: Exclude processes running under the Veeam.Backup.Service.exe image path and filter out events where the source directory is within the designated backup storage volume (e.g., D:\BackupData\).

• Antivirus Real-Time Scanning and Quarantine

  • Scenario: Microsoft Defender for Endpoint or Symantec Enterprise performs a scheduled deep scan during off-hours, locking, encrypting, or moving suspicious files to a quarantine folder. The rule may misinterpret these file state changes as malicious persistence mechanisms.
  • Filter/Exclusion: Create an exclusion list for the MsMpEng.exe (Defender) and Symantec Antivirus Client processes. Additionally, exclude any file operations occurring within the specific quarantine directory path (e.g., C:\ProgramData\Microsoft\Windows Defender\Support\Quarantine).

• Scheduled PowerShell Deployment Scripts

  • Scenario: An IT Operations team executes a nightly scheduled task using PowerShell.exe to deploy configuration updates via Group Policy. The script iterates through application folders, modifying registry keys and updating binary files, which triggers the rule’s persistence detection logic.
  • Filter/Exclusion: Filter events where the parent process is TaskScheduler.exe and the command line argument contains specific deployment identifiers (e.g., `-DeploymentID “NightlyConfig