PENightMarev13

Hunt Hypothesis

This rule identifies potential instances of the PENightMare malware family, which typically leverages PowerShell for initial access and lateral movement within Azure environments. Proactively hunting for this signature allows the SOC team to detect low-severity, stealthy intrusions before they escalate into more complex post-exploitation activities or data exfiltration.

YARA Rule

rule PENightMarev13
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 60 E8 00 00 00 00 5D B9 [4] 80 31 15 41 81 F9 }

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

• Scenario: A developer or DevOps engineer uses 7-Zip (or similar archivers like WinRAR) to compress a large folder of source code or logs for backup. The YARA rule may match specific byte patterns in the compressed container header or specific algorithm implementations within the executable.

  • Filter/Exclusion: Exclude processes where the parent process is 7z.exe, 7zG.exe, WinRAR.exe, or WinRAR.exe and the file extension is .7z, .rar, or .zip. Alternatively, exclude known archive tool binaries by their specific SHA256 hash or path (e.g., C:\Program Files\7-Zip\7z.exe).

• Scenario: An IT administrator runs Sysinternals tools (specifically PsExec or Process Explorer) to execute remote commands or inspect processes. The rule might trigger on the specific memory layout or string constants used by these Microsoft-provided utilities during process injection or handle enumeration.

  • Filter/Exclusion: Exclude processes where the executable name is PsExec.exe or Process.exe and the parent process is cmd.exe, powershell.exe, or wmic.exe. Verify the digital signature is “Microsoft Corporation” to ensure it is the legitimate Sysinternals binary.

• Scenario: A scheduled task runs vssadmin.exe (Volume Shadow Copy Service) to create a shadow copy before a backup job. The YARA rule could match the specific API calls or memory structures used by vssadmin when interacting with the VSS subsystem, especially if the rule targets common shadow copy manipulation techniques.

  • Filter/Exclusion: Exclude processes where the executable name is vssadmin.exe and the command line contains arguments like /create or /delete. Ensure the parent process is schtasks.exe or `