Detects c# red/black-team tools via typelibguid

Hunt Hypothesis

This hunt hypothesis identifies potential adversary activity by detecting C#-based red and black team tools through unique TypeLibGUID signatures within Azure Sentinel logs. Proactively hunting for these indicators allows the SOC team to distinguish legitimate security testing from malicious reconnaissance or tool deployment attempts that may otherwise blend into routine operational noise.

YARA Rule

rule HKTL_NET_GUID_SauronEye {
    meta:
        description = "Detects c# red/black-team tools via typelibguid"
        reference = "https://github.com/vivami/SauronEye"
        author = "Arnim Rupp"
        date = "2020-12-28"
    strings:
        $typelibguid0 = "0f43043d-8957-4ade-a0f4-25c1122e8118" ascii nocase wide
        $typelibguid1 = "086bf0ca-f1e4-4e8f-9040-a8c37a49fa26" 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 2 string patterns in its detection logic.

References

• https://github.com/vivami/SauronEye
• Source Rule

False Positive Guidance

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

• Scenario: Automated CI/CD Pipeline Execution

  • Context: Build agents (e.g., Azure DevOps, Jenkins) running on Windows servers frequently invoke C# compilation tasks or unit test runners that instantiate .NET assemblies with specific TypelibGUIDs matching known Red Team frameworks.
  • Filter/Exclusion: Create an exclusion based on the Process Name and User Account. Exclude processes named msbuild.exe, dotnet.exe, or vstest.console.exe when executed by service accounts such as NT SERVICE\BuildAgent or specific CI/CD user identities (e.g., svc-build-pipeline).

• Scenario: Enterprise Endpoint Protection Scanning

  • Context: Modern EDR solutions (like CrowdStrike Falcon, Microsoft Defender for Endpoint, or Carbon Black) often utilize C#-based management agents that load internal libraries containing GUIDs similar to those used by Red Team tools like Covenant or SharpUp.
  • Filter/Exclusion: Add a whitelist for the Parent Process Name. If the parent process is C:\Program Files\CrowdStrike\FalconSensor\csfalcon.exe (or equivalent EDR agent paths), suppress alerts regardless of the child process’s TypelibGUID.

• Scenario: Scheduled PowerShell Reporting Jobs

  • Context: IT Operations teams often run scheduled tasks using PowerShell (powershell.exe) to generate compliance reports or inventory data. These scripts frequently load C# helper classes (e.g., for Excel export or Active Directory queries) that trigger the detection logic.
  • Filter/Exclusion: Implement a filter based on Command Line Arguments and Scheduled Task Name. Exclude events where