Detects c# red/black-team tools via typelibguid

Hunt Hypothesis

This hunt hypothesis targets adversaries leveraging C#-based red and black team tools that expose unique TypeLibGUID artifacts to evade standard signature-based detection. Proactively hunting for these specific GUIDs in Azure Sentinel is critical because it enables the SOC team to identify sophisticated reconnaissance or post-exploitation activities that often bypass traditional endpoint protection mechanisms.

YARA Rule

rule HKTL_NET_GUID_clr_meterpreter {
    meta:
        description = "Detects c# red/black-team tools via typelibguid"
        reference = "https://github.com/OJ/clr-meterpreter"
        author = "Arnim Rupp"
        date = "2020-12-13"
    strings:
        $typelibguid0 = "6840b249-1a0e-433b-be79-a927696ea4b3" ascii nocase wide
        $typelibguid1 = "67c09d37-ac18-4f15-8dd6-b5da721c0df6" ascii nocase wide
        $typelibguid2 = "e05d0deb-d724-4448-8c4c-53d6a8e670f3" ascii nocase wide
        $typelibguid3 = "c3cc72bf-62a2-4034-af66-e66da73e425d" ascii nocase wide
        $typelibguid4 = "7ace3762-d8e1-4969-a5a0-dcaf7b18164e" ascii nocase wide
        $typelibguid5 = "3296e4a3-94b5-4232-b423-44f4c7421cb3" 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 6 string patterns in its detection logic.

References

• https://github.com/OJ/clr-meterpreter
• Source Rule

False Positive Guidance

Here are 4 specific false positive scenarios for the “Detects C# Red/Black-Team Tools via TypelibGUID” rule in an enterprise environment, along with suggested filters or exclusions:

• Scenario: Automated Patch Management Deployment

  • Context: Enterprise patching solutions like Microsoft Endpoint Configuration Manager (MECM/SCCM) or Ivanti frequently utilize C# agents to deploy updates. These agents often load specific .NET libraries containing unique typelibguid values that match the rule’s signature for red-team reconnaissance tools during the installation phase of Windows Updates or application patches.
  • Suggested Filter: Exclude processes originating from known patch management service accounts (e.g., NT SERVICE\ccmexec, IvantiAgent) and restrict the alert to exclude execution paths located within standard software distribution directories (e.g., C:\Program Files\Microsoft Configuration Manager\).

• Scenario: Scheduled SQL Database Maintenance Jobs

  • Context: Database administrators often schedule nightly maintenance tasks using SQL Server Agent. These jobs frequently invoke C# scripts or custom extensions to perform index rebuilding, backup verification, or data integrity checks. The underlying .NET runtime components for these specific SQL tools may share typelibguid identifiers with security assessment frameworks used by red teams.
  • Suggested Filter: Create an exclusion based on the parent process being sqlagent.exe and the execution path containing \Microsoft SQL Server\MSSQL*\MSSQL\Binn\. Additionally, filter for specific scheduled task names known to trigger these maintenance routines (e.g., “SQLServerMaintenanceTask”).

• Scenario: Endpoint Security Agent Self-Updates

  • Context: Major endpoint detection and response (EDR) platforms such as CrowdStrike, SentinelOne, or Carbon Black utilize C# components for their self-updating