Detects c# red/black-team tools via typelibguid

Hunt Hypothesis

This rule identifies potential adversary activity by detecting C#-based red and black team tools through their unique TypeLibGUID signatures within Azure Sentinel. Proactive hunting for these specific tool identifiers is essential to distinguish legitimate security operations from malicious reconnaissance or post-compromise tool deployment that may otherwise blend into routine system noise.

YARA Rule

rule HKTL_NET_GUID_k8fly {
    meta:
        description = "Detects c# red/black-team tools via typelibguid"
        reference = "https://github.com/zzwlpx/k8fly"
        author = "Arnim Rupp"
        date = "2020-12-29"
    strings:
        $typelibguid0 = "13b6c843-f3d4-4585-b4f3-e2672a47931e" 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/zzwlpx/k8fly
• 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 Build Pipeline Execution

  • Context: CI/CD agents (e.g., Jenkins, Azure DevOps) running build scripts that utilize .NET SDKs or MSBuild to compile C# applications. These processes often instantiate standard COM objects with known GUIDs during the compilation phase.
  • Filter/Exclusion: Exclude process paths matching C:\Program Files\Microsoft Visual Studio*\MSBuild\Bin\MSBuild.exe and C:\Windows\Microsoft.NET\Framework64\v4.0.30319\mscorsvw.exe, or filter by user context where the account is a dedicated service account (e.g., DOMAIN\CI-Build-Svc).

• Scenario: Endpoint Protection Scanning

  • Context: Enterprise antivirus solutions (such as CrowdStrike Falcon, Microsoft Defender for Endpoint, or Symantec) performing real-time scanning of .NET assemblies. The scanner’s internal engine often loads C# libraries to analyze code signatures, triggering the specific TypelibGUIDs associated with security tools.
  • Filter/Exclusion: Create an exclusion based on the parent process name (e.g., C:\Program Files\CrowdStrike\FalconSensor\csfalcon.exe or C:\Windows\System32\smss.exe) and exclude events where the command line contains keywords like “scan”, “update”, or “signature”.

• Scenario: Scheduled Office 365/SharePoint Provisioning Tasks

  • Context: Background jobs running on file servers or SharePoint farms that utilize PowerShell scripts wrapped in C# to manage OneDrive sync, permissions, or document libraries. These tasks frequently interact with the COM interface of Office