  Spectrum scarcity has been a major concern for achieving the desired quality of experience (QoE) in next-generation (5G/6G and beyond) networks supporting a massive volume of mobile and IoT devices with low-latency and seamless connectivity. Hence, spectrum sharing systems have been considered as a major enabler for next-generation wireless networks in meeting QoE demands. While most current coexistence solutions and standards focus on performance improvement and QoE optimization, the emerging security challenges of such network environments have been ignored in the literature. The security framework of standalone networks (either 5G or WiFi) assumes the ownership of entire network resources from spectrum to core functions. Hence, all accesses to the network shall be authenticated and authorized within the intra-network security system and is deemed illegal otherwise. However, coexistence network environments can lead to unprecedented security vulnerabilities and breaches as the standalone networks shall tolerate unknown and out-of-network accesses, specifically in the medium access. In this paper, for the first time in literature, we review some of the critical and emerging security vulnerabilities in the 5G/WiFi coexistence network environment which have not been observed previously in standalone networks. Specifically, independent medium access control (MAC) protocols and the resulting hidden node issues can result in exploitation such as service blocking, deployment of rogue base-stations, and eavesdropping attacks. We study potential vulnerabilities in the perspective of physical layer authentication, network access security, and cross-layer authentication mechanisms. This study opens a new direction of research in the analysis and design of a security framework that can address the unique challenges of coexistence networks. 
Security and Privacy vulnerabilities of 5G/6G and WiFi 6: Survey and   Research Directions from a Coexistence Perspective