CVE-2026-44322: free5GC's NEF 3gpp-pfd-management PATCH applications/{appId} panics on UDR access failure due to nil ProblemDetails dereference

free5GC’s NEF PATCH /3gpp-pfd-management/v1/{afId}/transactions/{transId}/applications/{appId} handler panics with a nil-pointer dereference when the upstream UDR call fails AND the consumer wrapper returns err != nil together with a nil *ProblemDetails. The handler’s errPfdData != nil branch builds its own problemDetailsErr correctly, but immediately after it reads problemDetails.Cause (the OTHER value, which is nil in this branch) and panics. Gin recovery converts the panic into HTTP 500, so a single PATCH against this endpoint returns 500 instead of the intended controlled error response whenever UDR access is failing.

This is a second-order bug: the trigger requires UDR access to be failing (e.g. NRF or UDR is unreachable, registration broken, transient network failure). The attacker does not directly control that condition, so this is scored as AC:H. Once the upstream condition exists, the trigger is a single PATCH request and is repeatable.

The HTTP request itself in v4.2.1 is reachable without an Authorization header because the underlying NEF 3gpp-pfd-management route group is mounted without inbound auth middleware (see free5gc/free5gc#858). So in the validation lab the entire trigger chain is unauthenticated end-to-end.