Detects c# red/black-team tools via typelibguid

Hunt Hypothesis

This hunt identifies potential adversary activity by detecting C#-based Red and Black team tools through their unique TypeLibGUID signatures within Azure Sentinel logs. Proactively hunting for these indicators allows the SOC to distinguish between legitimate security operations and stealthy malicious tooling that may mimic standard administrative processes.

YARA Rule

rule HKTL_NET_GUID_SharpDomainSpray {
    meta:
        description = "Detects c# red/black-team tools via typelibguid"
        reference = "https://github.com/HunnicCyber/SharpDomainSpray"
        author = "Arnim Rupp"
        date = "2020-12-13"
    strings:
        $typelibguid0 = "76ffa92b-429b-4865-970d-4e7678ac34ea" 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/HunnicCyber/SharpDomainSpray
• 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 servers (e.g., Jenkins, Azure DevOps) running C# compilation tasks or unit tests using dotnet CLI or MSBuild. These processes often load standard .NET assemblies that share the same TypeLibGUIDs as security tools like Sysmon or specific Red Team frameworks.
  • Filter/Exclusion: Exclude process paths matching known build agents (e.g., C:\Program Files\Microsoft Visual Studio*\MSBuild\Bin\MSBuild.exe, C:\Windows\Microsoft.NET\Framework64\v4.0.30319\mscorsvw.exe) and restrict the alert to specific service accounts (e.g., DOMAIN\CI-Build-Service).

• Scenario: Scheduled Antivirus or EDR Scans

  • Context: Enterprise Endpoint Detection and Response (EDR) agents (such as CrowdStrike Falcon, Carbon Black, or Microsoft Defender for Endpoint) perform scheduled deep scans. These agents utilize C# components to interface with the OS, triggering TypeLibGUIDs that overlap with Red Team tools like Cobalt Strike Beacons or SharpUp.
  • Filter/Exclusion: Create a whitelist based on the parent process name (e.g., C:\Program Files\CrowdStrike\FalconSensor\csfalcon.exe) and exclude events where the parent process is a known security service account running during maintenance windows (e.g., 02:00–04:00 UTC).

• Scenario: Office 365 / Microsoft Teams Background Updates

  • Context: The Microsoft Office Click-to-Run update service or Teams background processes often instantiate C#