<p>Vehicle-to-everything (V2X) communication enables vehicles to exchange information with other vehicles and infrastructure, such as traffic lights and road sensors. However, the communication channels used in V2X are susceptible to security threats, such as eavesdropping, message tampering, and denial-of-service (DoS) attacks. Therefore, V2X security is critical to ensure the confidentiality, integrity, and availability of communication in the transportation system. This paper provides an overview of the key security challenges in V2X communication and its security mechanisms. In addition, the various security testing methods are also addressed along with different security techniques adopted to protect V2X services. The performance metrics for evaluating the bandwidth, latency, dependability, and security of V2X communication are also investigated. This study leverages the tampering, repudiation, information disclosure, DoS, and elevation of privilege (STRIDE) threat model to identify backdoors and other loopholes in V2X communication. Further, the importance of standardization, interoperability, and scalability of security solutions across various V2X communication systems is also discussed, along with potential future developments and security challenges in V2X. This paper thus provides a comprehensive reference for researchers and academics in the fields of computer science, engineering, and transportation who seek to gain a thorough grasp of V2X systems and the security implications associated with them.</p>