Detects c# red/black-team tools via typelibguid

Hunt Hypothesis

This rule detects the execution of specialized C# Red and Black team tools by identifying unique TypeLibGUID signatures often associated with security testing or reconnaissance activities. Proactively hunting for these indicators in Azure Sentinel allows the SOC to distinguish between legitimate internal assessments and potential adversary use of similar tooling, ensuring that authorized testing does not obscure genuine threat signals.

YARA Rule

rule HKTL_NET_GUID_FileSearcher {
    meta:
        description = "Detects c# red/black-team tools via typelibguid"
        reference = "https://github.com/NVISO-BE/FileSearcher"
        author = "Arnim Rupp"
        date = "2020-12-28"
    strings:
        $typelibguid0 = "2c879479-5027-4ce9-aaac-084db0e6d630" ascii nocase wide
    condition:
        (uint16(0) == 0x5A4D and uint32(uint32(0x3C)) == 0x00004550) and any of them
}

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.

References

• https://github.com/NVISO-BE/FileSearcher
• Source Rule

False Positive Guidance

Here are 5 specific false positive scenarios for the “Detects c# red/black-team tools via typelibguid” rule, including suggested filters and exclusions:

• Scenario: Automated CI/CD Pipeline Execution

  • Context: Build agents (e.g., Azure DevOps or Jenkins running on Windows) frequently invoke C#-based build tools like MSBuild or NuGet.exe. These tools load specific COM type libraries during the compilation and dependency resolution phases, generating the exact typelibguid signatures associated with security tooling.
  • Filter/Exclusion: Create a process exclusion for known build service accounts (e.g., NT SERVICE\TeamFoundationBuildAgent) or exclude processes running within the specific directory path of the CI/CD agent installation (e.g., C:\Program Files\Microsoft Visual Studio\...).

• Scenario: Scheduled .NET Framework Updates

  • Context: The Windows Update service (wuauserv.exe) often triggers background tasks to install or repair .NET Framework components. During these operations, the system loads C# runtime libraries that match the typelibguid patterns used by Red/Black team tools, causing a spike in alerts during maintenance windows.
  • Filter/Exclusion: Implement a time-based exclusion for the rule during defined maintenance windows (e.g., 02:00–04:00 UTC on Sundays) or exclude events where the parent process is svchost.exe with the service name wuauserv.

• Scenario: Enterprise Antivirus Real-Time Scanning

  • Context: Endpoint Protection platforms (such as Microsoft Defender for Endpoint, CrowdStrike Falcon, or Symantec) utilize C# components to perform real-time heuristic analysis and signature updates. These internal modules often instantiate the same type libraries detected by the rule when scanning large files or