Toward a Robust Ingress for Open-Sourced 5G Core Network

The security of 5G networks hinges on the robustness and reliability of their software implementations from the core network infrastructure to end-user devices. Fortifying these networks against emerging threats and vulnerabilities requires rigorous testing. This article proposes a systematic approach for identifying flaws in 5G core network implementations. Focusing on the attack surfaces at 5G core network entry points, we identified flaws in handling the next-generation application protocol (NGAP) and nonaccess stratum (NAS) protocol with a fuzzer-in-the-middle (FitM) architecture that systematically evaluates multistage 5G core network protocol implementation; this architecture was applied to well-known open-source 5G core network implementations for evaluation. Specifically, the FitM architecture fuzzes valid user and base-station NAS and NGAP packets, which are then transmitted to the core network. In addition to recognizing 20 known implementation flaws, the FitM approach successfully recognized eight unknown flaws in various network functions in the core network implementations. The findings were reported to the developer community, and the issues have been fixed in most implementations. The proposed approach can be seamlessly integrated into the software development life cycle. The approach is both practical and extensible and can help communities develop more reliable core networks.