Detects c# red/black-team tools via typelibguid

Hunt Hypothesis

This detection rule identifies potential adversary activity by analyzing unique TypeLibGUID signatures associated with known C# red and black team reconnaissance or attack tools within Azure Sentinel. Proactively hunting for these specific GUID patterns allows the SOC team to distinguish legitimate security testing from genuine malicious tool usage, ensuring early visibility into covert operations that may otherwise blend in with standard administrative traffic.

YARA Rule

rule HKTL_NET_GUID_AsyncRAT_C_Sharp {
    meta:
        description = "Detects c# red/black-team tools via typelibguid"
        reference = "https://github.com/NYAN-x-CAT/AsyncRAT-C-Sharp"
        author = "Arnim Rupp"
        date = "2020-12-13"
    strings:
        $typelibguid0 = "619b7612-dfea-442a-a927-d997f99c497b" ascii nocase wide
        $typelibguid1 = "424b81be-2fac-419f-b4bc-00ccbe38491f" ascii nocase wide
        $typelibguid2 = "37e20baf-3577-4cd9-bb39-18675854e255" ascii nocase wide
        $typelibguid3 = "dafe686a-461b-402b-bbd7-2a2f4c87c773" ascii nocase wide
        $typelibguid4 = "ee03faa9-c9e8-4766-bd4e-5cd54c7f13d3" ascii nocase wide
        $typelibguid5 = "8bfc8ed2-71cc-49dc-9020-2c8199bc27b6" ascii nocase wide
        $typelibguid6 = "d640c36b-2c66-449b-a145-eb98322a67c8" ascii nocase wide
        $typelibguid7 = "8de42da3-be99-4e7e-a3d2-3f65e7c1abce" ascii nocase wide
        $typelibguid8 = "bee88186-769a-452c-9dd9-d0e0815d92bf" ascii nocase wide
        $typelibguid9 = "9042b543-13d1-42b3-a5b6-5cc9ad55e150" ascii nocase wide
        $typelibguid10 = "6aa4e392-aaaf-4408-b550-85863dd4baaf" 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 11 string patterns in its detection logic.

References

• https://github.com/NYAN-x-CAT/AsyncRAT-C-Sharp
• Source Rule

False Positive Guidance

Here are 3-5 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., Jenkins, Azure DevOps) running .NET-based test suites or deployment scripts often instantiate C# assemblies that share the same TypelibGUID as known Red Team tools like Lateral Movement Simulators or Credential Harvesters.
  • Filter/Exclusion: Exclude processes originating from specific CI/CD service accounts (e.g., SYSTEM, AzureDevOpsAgent) running on designated build server hostnames. Additionally, filter out events where the parent process is a known orchestrator like dotnet.exe or msbuild.exe.

• Scenario: Scheduled System Health Monitoring

  • Context: Enterprise monitoring solutions (e.g., SolarWinds, Datadog Agent) utilize C# libraries to query system state. These agents frequently load the same COM interfaces used by Black Team tools like Process Monitor Extensions or Network Traffic Analyzers, triggering alerts during their hourly scheduled scans.
  • Filter/Exclusion: Create an exclusion for known monitoring service processes (e.g., SolarWinds.Agent.exe, DatadogAgent.exe) running under the context of a “Health Check” scheduled task. Filter events where the command line contains keywords like /health-check or /status-report.

• Scenario: Microsoft Office Add-in Initialization

  • Context: Users launching Microsoft 365 applications (Outlook, Excel) often load third-party C# add-ins for productivity or security compliance. These add-ins frequently register with the same TypelibGUID as tools used by Red Teams to simulate user activity or document analysis.