Detects c# red/black-team tools via typelibguid

Hunt Hypothesis

This hunt targets adversaries leveraging C#-based red and black team tools that register unique TypeLib GUIDs to establish persistence or execute reconnaissance within the environment. Proactively hunting for these specific artifacts in Azure Sentinel is critical because their presence often indicates active threat emulation or advanced tool deployment that may bypass standard signature-based detections due to their low-severity classification.

YARA Rule

rule HKTL_NET_GUID_njCrypter {
    meta:
        description = "Detects c# red/black-team tools via typelibguid"
        reference = "https://github.com/0xPh0enix/njCrypter"
        author = "Arnim Rupp"
        date = "2020-12-13"
    strings:
        $typelibguid0 = "8a87b003-4b43-467b-a509-0c8be05bf5a5" ascii nocase wide
        $typelibguid1 = "80b13bff-24a5-4193-8e51-c62a414060ec" 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/0xPh0enix/njCrypter
• Source Rule

False Positive Guidance

Here are 5 specific false positive scenarios for the rule “Detects c# red/blue-team tools via typelibguid” in an enterprise environment, along with suggested filters or exclusions:

• Enterprise Endpoint Protection Scans

  • Scenario: The organization’s primary EDR agent (e.g., CrowdStrike Falcon, Carbon Black, or SentinelOne) utilizes a C#-based scanning engine that instantiates specific COM objects to analyze file integrity. During routine scheduled scans on workstations, the typelibguid associated with these internal C# libraries matches the signature of Red Team tools like Cobalt Strike or SharpUp.
  • Filter/Exclusion: Create an exclusion based on the parent process name (e.g., FalconSensorService.exe, cb.exe) and restrict the alert to only trigger if the parent is not a known security vendor executable.

• Microsoft Office Macro Execution

  • Scenario: Corporate finance or HR departments frequently use complex Excel workbooks containing VBA macros written in C# interop assemblies. When users open these templates (e.g., MonthlyBudgetTemplate.xlsx), the Excel process (EXCEL.EXE) loads a specific TypeLib GUID used by internal reporting tools, which overlaps with the GUIDs of Blue Team automation frameworks like PowerShell Empire or BloodHound.
  • Filter/Exclusion: Exclude events where the parent process is WINWORD.EXE, EXCEL.EXE, or OUTLOOK.EXE and the file path contains known corporate template directories (e.g., \\FileServer\Templates\HR).

• Automated Deployment Scripts via SCCM/Microsoft Endpoint Configuration Manager

  • Scenario: The IT Operations team runs nightly deployment jobs using Microsoft Endpoint Configuration Manager (MECM/SCCM). These jobs often invoke C# scripts to configure system settings