WindofCrypt10byDarkPressure

Hunt Hypothesis

This rule identifies the presence of the WindofCrypt ransomware variant, which encrypts files on Windows systems to extort victims, often deployed via phishing or initial access malware. Proactively hunting for this signature allows the SOC to detect early-stage infections or dormant payloads before encryption occurs, minimizing data loss and operational disruption within the Azure Sentinel environment.

YARA Rule

rule WindofCrypt10byDarkPressure
{
      meta:
		author="malware-lu"
strings:
		$a0 = {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}

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

• Legacy Application Maintenance: Administrators manually updating or patching legacy desktop applications (e.g., older versions of Adobe Creative Suite or specialized engineering CAD software) that rely on the DarkPressure compression engine or similar proprietary packers to reduce binary size.

  • Filter/Exclusion: Exclude files located in specific legacy application directories (e.g., C:\Program Files\LegacyApp\bin\) or add an exclusion for known parent processes like msiexec.exe or setup.exe when the file path matches the legacy app folder.

• Third-Party Backup Agent Installation: Installation or update of enterprise backup solutions (e.g., Veeam, Veritas NetBackup, or Acronis) where the installer package or agent binaries are packed using the DarkPressure algorithm to optimize deployment size over the network.

  • Filter/Exclusion: Exclude files whose parent process is a known backup installer (e.g., veeaminstaller.exe, nbackupsetup.exe) or exclude paths under standard backup agent directories (e.g., C:\Program Files\Veritas\, C:\Program Files (x86)\Veeam\).

• Scheduled .NET Assembly Optimization: Automated scheduled tasks (e.g., via Task Scheduler or schtasks.exe) that run .NET assembly optimizers or IL rewriters (e.g., ILSpy, NRefactory, or custom internal build scripts) which may compress or pack intermediate DLLs using DarkPressure before deployment to test environments.

  • Filter/Exclusion: Exclude files in temporary build directories (e.g., C:\Temp\builds\, C:\Users\svc_account\AppData\Local\Temp\) or exclude when the parent process is dotnet.exe, msbuild.exe, or vstest.console.exe.

• **CI/CD Pipeline