NWDAF-Assisted Zero-Trust Fault Diagnostics and Adaptive Response for 5G Core Networks

In 5G Core (5GC) networks, secure fault diagnosis should verify requesters and evidence while applying explicit policy checks to corrective actions. This letter proposes the Zero-Trust Fault Diagnostic Analytics Service (ZT-FDAS), which augments Network Data Analytics Function (NWDAF) services with request-scoped verification and adaptive responses. ZT-FDAS validates authorization, scope, integrity, provenance, and freshness of evidence before bounded LLM-guided graph traversal and deduplicated top-K ranking. A deterministic policy maps diagnoses and trust violations to monitor, step-up, restrict, or quarantine recommendations. An offline characterization of 1,049 resolved tickets assesses RCA graph construction, but not security effectiveness or diagnostic accuracy.