Detects c# red/black-team tools via typelibguid

Hunt Hypothesis

This detection rule identifies potential adversary activity by monitoring for C#-based Red and Blue team tools through their unique TypelibGUID signatures within Azure Sentinel. Proactively hunting for these specific tool identifiers allows the SOC team to distinguish legitimate security operations from malicious reconnaissance or lateral movement attempts that mimic standard administrative utilities.

YARA Rule

rule HKTL_NET_GUID_memscan {
    meta:
        description = "Detects c# red/black-team tools via typelibguid"
        reference = "https://github.com/nccgroup/memscan"
        author = "Arnim Rupp"
        date = "2020-12-28"
    strings:
        $typelibguid0 = "79462f87-8418-4834-9356-8c11e44ce189" 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/nccgroup/memscan
• 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 CI/CD Pipeline Build Agents

  • Context: Enterprise build servers (e.g., Jenkins, Azure DevOps) frequently compile .NET solutions using msbuild.exe or dotnet.exe. These processes often instantiate C# assemblies that generate specific Type Library GUIDs associated with testing frameworks like NUnit or xUnit, which the rule interprets as Red/Black team reconnaissance tools.
  • Filter/Exclusion: Exclude process paths containing \BuildAgents\, \Jenkins\, or \AzureDevOpsAgent\. Additionally, filter out events where the parent process is msbuild.exe running under a service account (e.g., NT SERVICE\TeamFoundationBuild).

• Scenario: Scheduled Endpoint Protection Scans

  • Context: Modern EDR agents (such as CrowdStrike Falcon or Microsoft Defender for Endpoint) utilize C# components to perform real-time heuristic analysis and signature updates. These background services often load Type Libraries that match the GUIDs of common security assessment tools, triggering alerts during their standard hourly scan cycles.
  • Filter/Exclusion: Create an exclusion based on process names FalconSensor.exe, MsMpEng.exe, or DefenderService.exe. Filter by excluding events where the command line arguments contain keywords like /scan, /update, or /heuristic.

• Scenario: Enterprise Office 365 Add-in Initialization

  • Context: When users launch Microsoft Outlook or Excel with heavy C#-based add-ins (e.g., Power BI, Teams integration, or custom CRM connectors), the host process (OUTLOOK.EXE or EXCEL.EXE) loads Type Libraries that mimic those used by Red