Detects c# red/black-team tools via typelibguid

Hunt Hypothesis

This hunt hypothesis identifies potential adversary activity by detecting C#-based red and black team tools through unique TypelibGUID signatures within Azure Sentinel logs. Proactively hunting for these indicators allows the SOC team to distinguish between legitimate security testing operations and suspicious reconnaissance or tool deployment by threat actors, ensuring early visibility into internal security exercises versus external threats.

YARA Rule

rule HKTL_NET_GUID_SweetPotato {
    meta:
        description = "Detects c# red/black-team tools via typelibguid"
        reference = "https://github.com/CCob/SweetPotato"
        author = "Arnim Rupp"
        date = "2020-12-28"
    strings:
        $typelibguid0 = "6aeb5004-6093-4c23-aeae-911d64cacc58" ascii nocase wide
        $typelibguid1 = "1bf9c10f-6f89-4520-9d2e-aaf17d17ba5e" 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/CCob/SweetPotato
• Source Rule

False Positive Guidance

Here are 5 specific false positive scenarios for the rule “Detects c# red/black-team tools via typelibguid”, including suggested filters and exclusions:

• Scenario: Automated CI/CD Pipeline Execution

  • Context: Build agents (e.g., Azure DevOps, Jenkins, or GitHub Actions runners) frequently compile C# projects during nightly builds. These processes often instantiate .NET assemblies that generate typelibguid events similar to those used by Red Team tools like Cobalt Strike Beacon or Mimikatz.
  • Filter/Exclusion: Exclude process paths matching known CI/CD agent binaries (e.g., C:\Program Files\Microsoft Visual Studio\*\MSBuild\*, C:\Windows\System32\msbuild.exe) and restrict the rule to exclude user accounts named SYSTEM or specific service accounts like CI-Build-Svc.

• Scenario: Scheduled Antivirus or EDR Scans

  • Context: Endpoint Detection and Response (EDR) agents such as CrowdStrike Falcon, SentinelOne, or Microsoft Defender for Endpoint often perform scheduled deep scans of the .NET framework. These scans involve loading various C# libraries that trigger typelibguid creation events, mimicking the behavior of Black Team tools like BloodHound collectors.
  • Filter/Exclusion: Create an exclusion based on the parent process name (e.g., falcon-sensor.exe, SentinelOneAgent.exe, or MsMpEng.exe) to prevent alerts when these security agents are the root cause of the event.

• Scenario: Office 365 ProPlus Add-in Initialization

  • Context: When users launch Microsoft Excel or PowerPoint, numerous C#-based add-ins (e.g., Power BI Desktop, **Adobe Acrobat PDF