Detects c# red/black-team tools via typelibguid

Hunt Hypothesis

This hypothesis posits that adversaries leverage C#-based Red and Black team tools with unique TypeLibGUID signatures to establish persistence or conduct reconnaissance within the environment. A proactive hunt is essential in Azure Sentinel to identify these specific tool artifacts early, enabling the SOC team to distinguish legitimate security operations from potential adversary activity before they escalate into higher-severity incidents.

YARA Rule

rule HKTL_NET_GUID_SharpRDP {
    meta:
        description = "Detects c# red/black-team tools via typelibguid"
        reference = "https://github.com/0xthirteen/SharpRDP"
        author = "Arnim Rupp"
        date = "2020-12-28"
    strings:
        $typelibguid0 = "f1df1d0f-ff86-4106-97a8-f95aaf525c54" 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/0xthirteen/SharpRDP
• Source Rule

False Positive Guidance

Here are 4 specific false positive scenarios for the “Detects C# Red/Black-Team Tools via TypelibGUID” rule, including suggested filters:

• Automated Build and CI/CD Pipeline Execution

  • Scenario: Enterprise build servers (e.g., Jenkins, Azure DevOps) frequently compile .NET solutions or execute unit tests using msbuild.exe or dotnet.exe. These processes often instantiate C# assemblies that register specific TypeLibGUIDs associated with testing frameworks like NUnit or xUnit, which may overlap with the GUIDs used by Red/Blue team attack simulation tools.
  • Suggested Filter: Exclude processes running under the context of known CI service accounts (e.g., NT SERVICE\Jenkins, DEVOPS-BUILD-SVC) and restrict detection to non-build server hostnames or specific IP ranges.

• Scheduled PowerShell Reporting Jobs

  • Scenario: IT Operations teams often schedule daily or weekly PowerShell scripts (powershell.exe or pwsh.exe) that import C# modules for asset inventory, license compliance checks, or security posture reporting. These scripts load custom C# assemblies with TypeLibGUIDs that mimic those found in penetration testing suites (e.g., tools like BloodHound or SharpUp).
  • Suggested Filter: Create an exclusion based on the parent process name (powershell.exe) and filter out events where the command line contains specific keywords such as “Inventory,” “Compliance,” or “Report”.

• Endpoint Management Agent Routine Scans

  • Scenario: Unified Endpoint Management (UEM) solutions like Microsoft Intune, SCCM, or specialized EDR agents perform routine health checks and policy enforcement. These agents often utilize C# components to query system configuration, triggering TypeLibGUID registration events that resemble the footprint of Red Team reconnaissance tools.
  • Suggested Filter: