The vulnerability is an improper error handling flaw in the NEF component of free5GC UDR. During parsing of network exposure function (NEF) requests, the component returns internal error details such as the invalid character position to remote clients. This exposes implementation specifics that could aid attackers in service fingerprinting, enabling more targeted attacks. The weakness maps to CWE-209 (Improper Output Neutralization for Security).

Affected systems are free5GC UDR deployments that use the Nnef_PfdManagement service, specifically versions up to and including 1.4.1. Any implementation of the free5GC stack that incorporates this NEF component is potentially exposed.

The CVSSv3 score of 6.6 indicates moderate severity. The EPSS score of less than 1% reflects a very low exploitation likelihood. The vulnerability is not listed in the CISA KEV catalog. Attackers can exploit the flaw remotely by sending malformed requests to the NEF endpoint; the server then leaks parsing error details. Because the information is second‑party and not actionable for direct code execution, the risk is primarily for reconnaissance. Patch or upgrade is recommended.