N Joy 10 NEX additional

Hunt Hypothesis

This YARA rule targets specific memory patterns associated with the N_Joy_10_NEX_additional component, indicating the presence of a known malware variant or its execution artifacts within a host. Proactively hunting for this signature allows the SOC team to identify low-severity infections that may be used for initial access or lateral movement, ensuring early containment before the adversary establishes a foothold in the Azure Sentinel environment.

YARA Rule

rule N_Joy_10_NEX_additional: PEiD
{
    strings:
        $a = { 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:
        $a 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

• Scenario: A legacy Java-based enterprise application (e.g., an older version of SAP NetWeaver or a custom internal portal) uses the NEX (Next) bytecode instruction within its JIT-compiled native helper libraries or JNI bridges to handle complex object traversal or state machine logic.

  • Filter/Exclusion: Exclude processes where the parent process is a known Java Virtual Machine (e.g., java.exe, jre.exe) and the file path contains \jre\ or \jdk\. Alternatively, exclude if the loaded module name matches known JRE library patterns (e.g., jvm.dll, jnet.dll).

• Scenario: A .NET application (e.g., a custom internal line-of-business tool or a third-party ERP client) uses the NEX opcode in its IL (Intermediate Language) assembly for advanced control flow, such as non-standard loop constructs or exception handling blocks that are not optimized away by the compiler.

  • Filter/Exclusion: Exclude processes where the executable is a .NET assembly (detected via PE header or dotnet.exe/dotnetcli.exe parent) and the file extension is .dll or .exe with a .NET manifest. Specifically, exclude if the process tree includes dotnet.exe or mscorwks.dll is loaded.

• Scenario: A scheduled task or service for a database backup utility (e.g., a custom script wrapping sqlbackup or a specific vendor tool like Veeam Agent) uses a native C++ helper library that employs NEX for efficient string parsing or data chunk processing during high-throughput I/O operations.

  • Filter/Exclusion: Exclude if the process name matches known backup/agent tools (e.g., VeeamAgent.exe, sqlbackup.exe, dbbackup.exe) and