With the application of artificial intelligent and 5G technology in the automotive industry, the intelligent connected vehicle came into being. It is a complex distributed heterogeneous system composed of a large number of electronic control units (ECUs) from different suppliers, and collaborates to control each ECU through the in-vehicle network protocol represented by CAN. An attacker could attack an intelligent connected vehicle through a variety of interfaces to penetrate the in-vehicle network, and then attack the in-vehicle network and its components such as ECU. Therefore, in-vehicle network security for intelligent connected vehicles has become one of the focuses of vehicle security research in recent years. On the basis of introducing the structure of intelligent connected vehicle, ECU, CAN bus and on-board diagnostic protocol, this paper firstly summarizes the research progress of reverse engineering technology for in-vehicle network protocols. It aims to obtain the implementation details of in-vehicle network protocols that are usually not disclosed in the automotive industry, and it is also a prerequisite for the implementation of in-vehicle network attack and defense. The remaining part is developed from two angles of attack and defense. On the one hand, the attack vectors and main attack technologies of in-vehicle network are summarized, including the attack technologies implemented through physical access and remote access, as well as the attack technologies implemented against ECU and CAN bus. On the other hand, the existing in-vehicle network defense technologies are discussed, including the intrusion detection technology based on different feature extraction and machine learning methods, and the security enhancement technology of in-vehicle network protocols based on cryptography approaches. Finally, the future research direction is prospected.