Detects .NET red/black-team tools via name

Hunt Hypothesis

This detection rule identifies the execution of known .NET-based security testing utilities by analyzing process names to distinguish between legitimate Red Team and Black Team activities. Proactive hunting for these specific tool signatures in Azure Sentinel is essential to differentiate authorized security assessments from potential adversary reconnaissance that mimics similar .NET frameworks, thereby reducing false positives during incident response.

YARA Rule

rule HKTL_NET_NAME_C2Bridge {
    meta:
        description = "Detects .NET red/black-team tools via name"
        reference = "https://github.com/cobbr/C2Bridge"
        author = "Arnim Rupp"
        date = "2021-01-22"
    strings:
        $name = "C2Bridge" ascii wide
        $compile = "AssemblyTitle" ascii wide
    condition:
        (uint16(0) == 0x5A4D and uint32(uint32(0x3C)) == 0x00004550) and all 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/cobbr/C2Bridge
• Source Rule

False Positive Guidance

Here are 5 specific false positive scenarios for the rule “Detects .NET red/blue-team tools via name,” along with suggested filters or exclusions:

• Scenario: A System Administrator manually launches Sysmon (a Microsoft tool) to review event logs on a Domain Controller.

  • Context: The detection logic flags the executable name sysmon64.exe as a potential Red Team reconnaissance tool because it is a common .NET-based security utility often used by both defenders and attackers.
  • Filter/Exclusion: Exclude processes where the parent process is svchost.exe or powershell.exe running under the NT SERVICE\ context, specifically targeting the path C:\Program Files\Sysmon\sysmon64.exe.

• Scenario: An automated nightly backup job executes Robocopy via a PowerShell script that invokes a .NET wrapper named BackupAgent.exe.

  • Context: The rule triggers because BackupAgent.exe contains “Agent” in its name, which is a common naming convention for Red Team lateral movement tools. This occurs on file servers during the 2:00 AM maintenance window.
  • Filter/Exclusion: Create an exclusion based on the scheduled task ID (e.g., Microsoft\Windows\Backup\Daily) or filter by process path C:\Program Files\Enterprise Backup\BackupAgent.exe combined with a time-based constraint (exclude events between 01:00 and 04:00).

• Scenario: The IT Helpdesk uses the remote management tool PDQ Deploy to push software updates, which spawns a .NET process named DeployEngine.exe.

  • Context: During mass deployment windows, multiple endpoints simultaneously launch this tool. The rule interprets the widespread execution of a .NET tool with “Engine” in the name as