NJoy10NEX

Hunt Hypothesis

This detection identifies potential malicious activity associated with the NJoy10NEX signature through YARA scanning, indicating the presence of specific file patterns often linked to known threat actors or benign software anomalies. A proactive hunt is recommended in Azure Sentinel to validate these low-severity alerts against baseline behavior, ensuring that false positives are filtered out while early-stage threats are not overlooked before they escalate.

YARA Rule

rule NJoy10NEX
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 55 8B EC 83 C4 F0 B8 9C 3B 40 00 E8 8C FC FF FF 6A 00 68 E4 39 40 00 6A 0A 6A 00 E8 40 FD FF FF E8 EF F5 FF FF 8D 40 00 }

condition:
		$a0 at pe.entry_point
}

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 1 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 5 specific false positive scenarios for the NJoy10NEX detection rule in an enterprise environment, along with recommended filters or exclusions:

• Scenario: Legitimate execution of the Microsoft Office Click-to-Run update service (OfficeClickToRun.exe) during scheduled maintenance windows. This process often spawns child processes that match the NJoy10NEX signature due to shared DLL dependencies or similar memory patterns.

  • Filter/Exclusion: Add a path-based exclusion for C:\Program Files\Microsoft Office\root\Office16\ and exclude process names containing OfficeClickToRun.exe.

• Scenario: Automated deployment of security patches via SCCM (System Center Configuration Manager) or Intune where the ccmsetup.exe installer launches a temporary helper utility that mimics the behavior profile detected by NJoy10NEX.

  • Filter/Exclusion: Create an exclusion rule for processes launched directly by ccmexec.exe (SCCM) and Microsoft.IntuneManagementAgent.exe, specifically filtering out events where the parent process is one of these known management agents.

• Scenario: Execution of a scheduled PowerShell script (powershell.exe) running a custom backup or reporting job that utilizes the .NET framework, which often triggers the YARA rule due to similar string patterns in memory.

  • Filter/Exclusion: Exclude events where the command line contains specific keywords such as --backup, --report, or paths pointing to C:\Scripts\ and D:\Automation\. Additionally, whitelist the hash of the known good script file.

• Scenario: Routine operation of CrowdStrike Falcon or SentinelOne agents performing real-time scanning, where their internal update modules (FalconSensor.exe or S1Service.exe) load components that