Modeling 5G Threat Scenarios for Critical Infrastructure Protection.

Fifth-generation cellular networks (5G) are currently being deployed by mobile operators around the globe. 5G is an enabler for many use cases and improves security and privacy over 4G and previous network generations. However, as recent security research has revealed, the 5G standard still has technical security weaknesses for attackers to exploit. In addition, the migration from 4G to 5G systems takes place by first deploying 5G solutions in a non-standalone (NSA) manner, where the first step of the 5G deployment is restricted to the new radio aspects of 5G. At the same time, the control of user equipment is still based on 4G protocols; that is, the core network is still the legacy 4G evolved packet core (EPC) network. As a result, many security vulnerabilities of 4G networks are still present in current 5G deployments. To stimulate the discussion about the security risks in current 5G networks, particularly regarding critical infrastructures, we model possible threats according to the STRIDE threat classification model. We derive a risk matrix based on the likelihood and impact of eleven threat scenarios (TS) that affect the radio access and the network core. We estimate that malware or software vulnerabilities on the 5G base station constitute the most impactful threat scenario, though not the most probable. In contrast, a scenario where compromised cryptographic keys threaten communications between network functions is both highly probable and highly impactful. To improve the 5G security posture, we discuss possible mitigations and security controls. Our analysis is generalizable and does not depend on the specifics of any particular 5G network vendor or operator.