Detects c# red/black-team tools via typelibguid

Hunt Hypothesis

This rule identifies potential adversary activity by monitoring for C# Red and Black team tools through their unique TypeLibGUID signatures within Azure Sentinel. Proactive hunting for these specific tool identifiers is essential to distinguish legitimate security operations from malicious reconnaissance or lateral movement attempts that mimic standard administrative utilities.

YARA Rule

rule HKTL_NET_GUID_Random_CSharpTools {
    meta:
        description = "Detects c# red/black-team tools via typelibguid"
        reference = "https://github.com/xorrior/Random-CSharpTools"
        author = "Arnim Rupp"
        date = "2020-12-21"
    strings:
        $typelibguid0 = "f7fc19da-67a3-437d-b3b0-2a257f77a00b" ascii nocase wide
        $typelibguid1 = "47e85bb6-9138-4374-8092-0aeb301fe64b" ascii nocase wide
        $typelibguid2 = "c7d854d8-4e3a-43a6-872f-e0710e5943f7" ascii nocase wide
        $typelibguid3 = "d6685430-8d8d-4e2e-b202-de14efa25211" ascii nocase wide
        $typelibguid4 = "1df925fc-9a89-4170-b763-1c735430b7d0" ascii nocase wide
        $typelibguid5 = "817cc61b-8471-4c1e-b5d6-c754fc550a03" ascii nocase wide
        $typelibguid6 = "60116613-c74e-41b9-b80e-35e02f25891e" 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 7 string patterns in its detection logic.

References

• https://github.com/xorrior/Random-CSharpTools
• Source Rule

False Positive Guidance

Here are 5 specific false positive scenarios for the “Detects c# red/black-team tools via typelibguid” rule, along with recommended filters or exclusions:

• Scenario: Automated CI/CD Pipeline Execution

  • Context: Build servers (e.g., Jenkins, Azure DevOps) frequently compile C# projects using msbuild.exe or dotnet.exe. These processes often load standard .NET assembly libraries that share the same typelibguid signatures as known red-team tools like SharpUp or Bloodhound.
  • Filter/Exclusion: Exclude alerts where the process name is msbuild.exe, dotnet.exe, or vstt_build.exe AND the parent process is a CI service account (e.g., SYSTEM, NT SERVICE\Jenkins).

• Scenario: Office 365 ProPlus Background Updates

  • Context: The Microsoft Office Click-to-Run update engine (OfficeC2RClient.exe) or background sync services often instantiate C# components that utilize specific Type Library GUIDs identical to those found in tools like SharpHound or PowerSploit. This is common during off-hours maintenance windows.
  • Filter/Exclusion: Create a whitelist for the process path containing \Microsoft Office\ClickToRun\OfficeC2RClient.exe and exclude alerts occurring between 01:00 and 05:00 UTC on weekdays.

• Scenario: Enterprise Antivirus Heuristic Scanning

  • Context: Endpoint protection agents (e.g., CrowdStrike, SentinelOne) perform deep heuristic scans of C# applications. During these scans, the AV engine may inject DLLs or spawn helper processes that mimic the typelibguid patterns of black-team tools like Mimikatz or LaZagne.
  • **Filter