Detects .NET red/black-team tools via typelibguid

Hunt Hypothesis

This rule identifies the execution of known .NET-based red and blue team utilities by analyzing unique typelibGUID signatures within Azure Sentinel logs. Proactively hunting for these artifacts allows the SOC to distinguish between legitimate security operations and potential adversary activity that mimics standard tooling behavior, thereby reducing false positives and enhancing visibility into internal reconnaissance efforts.

YARA Rule

rule HKTL_NET_GUID_SharpDir {
    meta:
        description = "Detects .NET red/black-team tools via typelibguid"
        reference = "https://github.com/jnqpblc/SharpDir"
        author = "Arnim Rupp"
        date = "2021-01-21"
    strings:
        $typelibguid0 = "c7a07532-12a3-4f6a-a342-161bb060b789" 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/jnqpblc/SharpDir
• Source Rule

False Positive Guidance

Here are 4 specific false positive scenarios for the Detects .NET red/black-team tools via typelibguid rule, including suggested filters and exclusions:

• Scenario: Scheduled Office 365 ProPlus Update Tasks

  • Context: The Microsoft Office Click-to-Run service (OfficeClickToRun.exe) or the Background Intelligent Transfer Service (BITS) often executes .NET assemblies during scheduled update cycles. These processes utilize specific typelibguid signatures that overlap with red-team tools like Covenant or SharpUp.
  • Filter/Exclusion: Exclude process names containing OfficeClickToRun.exe, msiexec.exe, and bitsadmin.exe running under the SYSTEM or NT SERVICE\* accounts, specifically when the command line contains arguments related to “update,” “patch,” or “clicktorun”.

• Scenario: Enterprise Endpoint Protection Scans

  • Context: Major EDR solutions (e.g., Microsoft Defender for Endpoint, CrowdStrike Falcon, or SentinelOne) utilize .NET-based scanning engines. When these agents perform real-time file monitoring or on-demand scans, they load internal .NET libraries that generate typelibguid signatures indistinguishable from black-team tools like BloodHound or SharpUp.
  • Filter/Exclusion: Create a whitelist for known EDR process paths (e.g., C:\Program Files\Microsoft Defender\MsMpEng.exe, C:\Program Files\CrowdStrike\FalconSensor.exe) and exclude events where the parent process is one of these security agents.

• Scenario: Automated PowerShell Reporting Jobs

  • Context: IT Operations teams often run scheduled PowerShell scripts (using pwsh.exe or powershell.exe) to generate compliance reports, inventory hardware, or manage Active Directory objects. These scripts frequently instantiate .NET assemblies with standard library GUID