  Cellular-Vehicle to Everything (C-V2X) aims at resolving issues pertaining to
the traditional usability of Vehicle to Infrastructure (V2I) and Vehicle to
Vehicle (V2V) networking. Specifically, C-V2X lowers the number of entities
involved in vehicular communications and allows the inclusion of
cellular-security solutions to be applied to V2X. For this, the evolvement of
LTE-V2X is revolutionary, but it fails to handle the demands of high
throughput, ultra-high reliability, and ultra-low latency alongside its
security mechanisms. To counter this, 5G-V2X is considered as an integral
solution, which not only resolves the issues related to LTE-V2X but also
provides a function-based network setup. Several reports have been given for
the security of 5G, but none of them primarily focuses on the security of
5G-V2X. This article provides a detailed overview of 5G-V2X with a
security-based comparison to LTE-V2X. A novel Security Reflex Function
(SRF)-based architecture is proposed and several research challenges are
presented related to the security of 5G-V2X. Furthermore, the article lays out
requirements of Ultra-Dense and Ultra-Secure (UD-US) transmissions necessary
for 5G-V2X.
