VxCIHVersion12TTITWIN95CIH

Hunt Hypothesis

This hypothesis targets the presence of the VxCIHVersion12TTITWIN95CIH YARA signature, which indicates a specific variant of the VBCI (VirusBench CIH) malware family often used for testing or as a component in complex infection chains. Proactively hunting for this signature in Azure Sentinel allows the SOC to identify low-severity but potentially persistent threats that may be overlooked by standard behavioral detections, ensuring comprehensive coverage against known malware artifacts in the environment.

YARA Rule

rule VxCIHVersion12TTITWIN95CIH
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 55 8D [3] 33 DB 64 87 03 E8 [4] 5B 8D }

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 .NET Framework Compilation on Build Servers: The rule likely targets specific version strings or binary patterns associated with older .NET implementations or specific compiler artifacts. Legitimate build pipelines using older versions of MSBuild or specific .NET 1.1/2.0 targeting frameworks may generate binaries containing these version markers.

  • Filter/Exclusion: Exclude files located in standard build output directories (e.g., C:\Builds\, C:\Artifacts\) or exclude processes spawned by MSBuild.exe or dotnet build commands that are part of known CI/CD pipeline service accounts.

• Legacy Java Applet or Swing Application Updates: If the rule inspects for specific version strings (like “1.2” or “95”) within executable resources, legacy Java applications or applets that embed version metadata in their JARs or native wrappers might trigger this. This is common in financial or industrial control systems that rely on older Java versions.

  • Filter/Exclusion: Exclude processes running from java.exe or javaw.exe where the command line arguments include -jar or -cp pointing to known application directories, or exclude files with the .jar extension if the rule is file-based.

• Scheduled Backup or Snapshot Jobs with Versioned Binaries: Enterprise backup solutions (like Veeam, Commvault, or Veritas) or snapshot tools may copy or restore binaries that contain specific version strings. If the rule scans memory or disk for these strings, restored legacy application binaries (e.g., old versions of Outlook, Exchange tools, or custom line-of-business apps) could match.

  • Filter/Exclusion: Exclude processes associated with known backup agents (e.g., VeeamBackup.exe, cvpp.exe) or exclude file paths within backup scratch directories (e.g., `C:\ProgramData\Veeam