Detects c# red/black-team tools via typelibguid

Hunt Hypothesis

This rule identifies potential adversary activity by detecting C#-based red and black team tools through their unique TypeLibGUID signatures within Azure Sentinel logs. Proactive hunting for these specific identifiers is essential to distinguish legitimate security testing from malicious reconnaissance or tool deployment that may otherwise evade standard signature-based detections.

YARA Rule

rule HKTL_NET_GUID_PortTran {
    meta:
        description = "Detects c# red/black-team tools via typelibguid"
        reference = "https://github.com/k8gege/PortTran"
        author = "Arnim Rupp"
        date = "2020-12-29"
    strings:
        $typelibguid0 = "3a074374-77e8-4312-8746-37f3cb00e82c" ascii nocase wide
        $typelibguid1 = "67a73bac-f59d-4227-9220-e20a2ef42782" 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 2 string patterns in its detection logic.

References

• https://github.com/k8gege/PortTran
• Source Rule

False Positive Guidance

Here are 4 specific false positive scenarios for the “Detects C# Red/Black-Team Tools via TypelibGUID” rule, including suggested filters and exclusions:

• Scenario: Automated Build Pipelines (Jenkins/GitLab CI)

  • Context: Continuous Integration servers frequently execute C# compilation tasks using msbuild.exe or custom build agents that load specific .NET assemblies. These processes often instantiate the same TypelibGUIDs used by security tools during the build phase, triggering alerts on build nodes.
  • Filter/Exclusion: Exclude processes running under the service account of the CI server (e.g., Jenkins, GitLab Runner) or filter by process path containing \build\ or \agent\. Additionally, add a time-based exclusion for known maintenance windows (e.g., 02:00–04:00 UTC).

• Scenario: Microsoft Defender for Endpoint (MDE) Self-Scanning

  • Context: The MDE sensor itself is written in C# and utilizes internal libraries that share the same TypelibGUIDs as external Red/Black team tools. When the sensor performs a scheduled full scan or updates its definition database, it generates these GUIDs internally, causing self-detection alerts.
  • Filter/Exclusion: Create an exclusion for process names MsMpEng.exe and SenseService.exe. Alternatively, exclude events where the parent process is the MDE sensor itself to prevent recursive detection.

• Scenario: Office 365 ProPlus Background Updates

  • Context: Enterprise environments with Microsoft Office installed often run background update tasks (OfficeClickToRun.exe or UpdateService.exe) that load C# components for license verification and feature installation. These components utilize standard .NET TypelibGUIDs that overlap with the detection logic for security tools.