Detects c# red/black-team tools via typelibguid

Hunt Hypothesis

This hunt targets adversaries leveraging C#-based red and black team tools that expose unique typelibguid artifacts to establish persistence or conduct reconnaissance within Azure environments. Proactively hunting for these specific identifiers allows the SOC team to distinguish legitimate administrative activity from stealthy tool deployment, ensuring early identification of potential lateral movement or post-exploitation phases even when initial rule severity is low.

YARA Rule

rule HKTL_NET_GUID_Obfuscator {
    meta:
        description = "Detects c# red/black-team tools via typelibguid"
        reference = "https://github.com/3xpl01tc0d3r/Obfuscator"
        author = "Arnim Rupp"
        date = "2020-12-13"
    strings:
        $typelibguid0 = "8fe5b811-a2cb-417f-af93-6a3cf6650af1" 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/3xpl01tc0d3r/Obfuscator
• 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:

• Microsoft Office Click-to-Run Updates

  • Scenario: The Microsoft Office installation service (OfficeClickToRun.exe) or background update tasks frequently instantiate C# assemblies that register specific TypeLib GUIDs during scheduled maintenance windows. These legitimate updates often mimic the behavior of reconnaissance tools by probing system libraries.
  • Suggested Filter: Exclude processes with ImageName matching *OfficeClickToRun.exe, *setup.exe (Microsoft Office path), and *OneDrive.exe where the parent process is svchost.exe or a known Microsoft update service.

• Enterprise Endpoint Protection Scans

  • Scenario: Major EDR solutions like CrowdStrike Falcon, Carbon Black, or SentinelOne utilize C# components for their real-time scanning engines and policy enforcement modules. During full system scans or definition updates, these tools load internal libraries that generate the specific TypeLib GUIDs associated with security tooling.
  • Suggested Filter: Create an exclusion list based on ImageName containing known EDR vendor signatures (e.g., *FalconSensor.exe, *cb.exe, *SentinelOneAgent.exe) and restrict the rule to only trigger when these processes are running under non-admin service accounts.

• Automated PowerShell Deployment Scripts

  • Scenario: IT Operations teams often run scheduled PowerShell jobs (e.g., via Task Scheduler) that invoke C# scripts for configuration management, software deployment, or inventory collection using tools like Ansible, Chef, or custom internal automation suites. These scripts load the .NET runtime and register TypeLib GUIDs indistinguishable from red-team enumeration tools.

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