Detects .NET red/black-team tools via name

Hunt Hypothesis

This rule identifies the execution of known .NET-based Red and Blue team utility names to distinguish legitimate security operations from potential adversary tooling that mimics these signatures. A proactive hunt is essential in Azure Sentinel to validate these detections against actual user activity, ensuring that benign internal tools are not overlooked while malicious actors leveraging similar naming conventions are promptly identified.

YARA Rule

rule HKTL_NET_NAME_njRAT_0_7d_Stub_CSharp {
    meta:
        description = "Detects .NET red/black-team tools via name"
        reference = "https://github.com/NYAN-x-CAT/njRAT-0.7d-Stub-CSharp"
        author = "Arnim Rupp"
        date = "2021-01-22"
    strings:
        $name = "njRAT-0.7d-Stub-CSharp" 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/NYAN-x-CAT/njRAT-0.7d-Stub-CSharp
• Source Rule

False Positive Guidance

Here are 4 specific false positive scenarios for the rule “Detects .NET red/blue-team tools via name,” including suggested filters and exclusions:

• Scenario: Automated Compliance Scanning by Admin Tools

  • Context: Enterprise security teams often deploy automated compliance scanners (e.g., Tenable Nessus, Qualys, or custom PowerShell scripts) that utilize .NET assemblies to enumerate system configurations. These tools frequently spawn processes with names like ComplianceEngine.exe or AuditCollector.dll which match the “red/black-team” naming pattern of security tools.
  • Suggested Filter/Exclusion: Create an exclusion based on the Process Name and Parent Process. Exclude alerts where the process name matches known scanner binaries (e.g., Nessus.exe, QualysPCAgent.exe) OR where the parent process is a scheduled task service (TaskHost.exe or svchost.exe) running under a dedicated service account (e.g., DOMAIN\CompScanSvc).

• Scenario: Scheduled .NET Backup and Migration Jobs

  • Context: IT operations teams frequently use custom .NET applications for data migration, backup verification, or asset inventory. A common example is a nightly job running an application named AssetInventoryTool.exe or DataSyncAgent.exe. Because these tools are built on the .NET framework and perform deep system introspection similar to red-team tools, they trigger false positives during their scheduled execution windows (e.g., 02:00 – 04:00 AM).
  • Suggested Filter/Exclusion: Implement a time-based exclusion combined with a User Context filter. Exclude alerts occurring between 01:00 and 05:00 local time where the Logon User is a known service account (e.g., DOMAIN\BackupSvc) and the