Detects .NET red/black-team tools via typelibguid

Hunt Hypothesis

This hunt hypothesis identifies adversaries leveraging custom or known .NET-based offensive and defensive tools by analyzing unique TypeLibGUID signatures within process execution events. Proactively hunting for these indicators in Azure Sentinel allows the SOC team to distinguish between legitimate administrative activity and potential red-team exercises or stealthy threat actor tooling that may otherwise blend into standard background noise.

YARA Rule

rule HKTL_NET_GUID_AtYourService {
    meta:
        description = "Detects .NET red/black-team tools via typelibguid"
        reference = "https://github.com/mitchmoser/AtYourService"
        author = "Arnim Rupp"
        date = "2021-01-21"
    strings:
        $typelibguid0 = "bc72386f-8b4c-44de-99b7-b06a8de3ce3f" 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/mitchmoser/AtYourService
• Source Rule

False Positive Guidance

Here are 3-5 specific false positive scenarios for the rule “Detects .NET red/black-team tools via typelibguid,” including suggested filters and exclusions:

• Scenario: Microsoft Office 365 ProPlus Background Updates

  • Context: The OfficeClickToRun.exe or Microsoft.Update.Service processes frequently instantiate .NET assemblies with specific TypeLibGUIDs during scheduled background updates, document indexing, or OneDrive synchronization. These legitimate administrative tasks often mimic the footprint of red-team reconnaissance tools like BloodHound or SharpUp.
  • Suggested Filter/Exclusion: Exclude events where the ImageName contains OfficeClickToRun.exe, OneDrive.exe, or Microsoft.Update.Service.exe. Additionally, filter out TypeLibGUIDs known to belong to standard Office COM components (e.g., 000209FF-0000-0000-C000-000000000046 for Excel).

• Scenario: Scheduled PowerShell Automation Scripts

  • Context: Enterprise IT operations often rely on scheduled tasks (Task Scheduler) running custom .NET-based PowerShell scripts or tools like Pester for compliance testing. When these scripts load specific .NET libraries to query Active Directory or manage configurations, they generate TypeLibGUIDs that overlap with black-team forensics tools such as PowerSploit modules or SharpHound.
  • Suggested Filter/Exclusion: Create an exclusion rule based on the AccountName (e.g., NT SERVICE\TaskScheduler, SYSTEM) and CommandLine containing keywords like -NoProfile, -NonInteractive, or specific script paths located in known administrative directories (e.g., C:\ProgramData\Scripts\).

• **Scenario: Endpoint Detection and Response (EDR) Agent Sc