Detects c# red/black-team tools via typelibguid

Hunt Hypothesis

This hunt hypothesis targets adversaries leveraging C#-based red and black team tools that register unique TypeLibGUIDs to establish persistence or execute reconnaissance within the environment. Proactively hunting for these specific GUID signatures in Azure Sentinel enables the SOC team to identify legitimate tooling versus malicious activity early, reducing noise from false positives while uncovering stealthy post-compromise behaviors.

YARA Rule

rule HKTL_NET_GUID_WindowsRpcClients {
    meta:
        description = "Detects c# red/black-team tools via typelibguid"
        reference = "https://github.com/tyranid/WindowsRpcClients"
        author = "Arnim Rupp"
        date = "2020-12-28"
    strings:
        $typelibguid0 = "843d8862-42eb-49ee-94e6-bca798dd33ea" ascii nocase wide
        $typelibguid1 = "632e4c3b-3013-46fc-bc6e-22828bf629e3" ascii nocase wide
        $typelibguid2 = "a2091d2f-6f7e-4118-a203-4cea4bea6bfa" ascii nocase wide
        $typelibguid3 = "950ef8ce-ec92-4e02-b122-0d41d83065b8" ascii nocase wide
        $typelibguid4 = "d51301bc-31aa-4475-8944-882ecf80e10d" ascii nocase wide
        $typelibguid5 = "823ff111-4de2-4637-af01-4bdc3ca4cf15" ascii nocase wide
        $typelibguid6 = "5d28f15e-3bb8-4088-abe0-b517b31d4595" 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/tyranid/WindowsRpcClients
• 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 Backup & Recovery Operations

  • Context: Enterprise backup solutions like Veeam Backup & Replication or Commvault utilize C# agents that interact with the Windows Registry to manage job states. These agents often instantiate COM objects via specific typelibguid values during scheduled nightly backups, mimicking the behavior of Red/Black team reconnaissance tools.
  • Suggested Filter: Exclude processes where the executable path matches known backup agent directories (e.g., C:\Program Files\Veeam\Backup and Replication\Agent\) AND the parent process is a recognized service host (e.g., svchost.exe with specific service names like VeeamTransport).

• Scenario: Endpoint Security & Antivirus Scans

  • Context: Modern EDR platforms such as CrowdStrike Falcon, SentinelOne, or Microsoft Defender for Endpoint frequently use C# components to perform real-time file indexing and threat hunting. These tools often load typelibs to query system state, which can trigger the rule when they scan specific .NET assemblies or registry keys associated with security policies.
  • Suggested Filter: Create an exclusion based on the ImageName containing known EDR vendor names (e.g., falcon.sys, SentinelOne.exe) and filter out events where the CommandLine includes keywords related to “scan,” “index,” or “policy update.”

• Scenario: Software Deployment & Patching Agents

  • Context: Configuration management tools like Microsoft System Center Configuration Manager (SCCM/MECM) or Ansible Tower agents run scheduled jobs to deploy patches and software. These agents utilize C