## 4 Security Issues and Solutions for CAVs
### Cyber-Attacks on Intra-Vehicle Systems
#### 4.1.3 Open Issues of Intra-Vehicle System Security  
In practice, there are many limits to successfully launching a cyber-attack on CAVs. For example, when the attacker tries to compromise the communication module, the attack needs to bypass the verification or integrity check of the system, which may activate the alarm. Moreover, some patterns of vehicles do not allow outside devices to send a message to the bus system when the vehicle is moving. Even so, security must be built into the system before the manufacturing of a vehicle and the wide deployment of CAVs. On one hand, to maintain the various connectivity to vehicle systems without exposing vulnerabilities of the system, effective access control must be implemented on the system to guarantee secure information input. The system must grant selective access to its components. For example, when a vehicle is moving, the module which can send messages to the CAN bus should forbid any reboot. Furthermore, the system must ensure that only authorized devices can gain limited access to certain types of its components. Each time a new connectivity is created between the system and an outside device, integrity and verification must be implemented [27]. The principle of least privilege should be applied while providing access to the connected device. In addition, in terms of software design of the system, buffer overflow, string format vulnerabilities should be avoided to prevent connected devices from modifying the system when the situations occur. \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Type** & **Description** & **Attacks/Consequences** & **Defenses** \\ \hline \multirow{4}{*}{DoS} & Introduce the topmost priority nonsense message frequently to systems. & (1) & Cause flooding. \\  & & (2) & Hinder regular services. \\  & & (3) & Detect existing security loopholes of system. & (1) & Identify security loopholes earlier. \\  & & & (2) & Verify the fix/ update files. \\ \hline \multirow{4}{*}{Fuzzing attack} & Massive amounts of random data can be inputted to the system. & (1) & Crash the system. & (3) & Combination of authentication and integrity verification. \\ \cline{1-1}  & Carry out malicious modifications of code; inject malicious messages to the bus system. & (1) & Override certain functions. & (1) & Authorize connected devices. \\ \hline \multirow{4}{*}{Replay attack} & Retransmit eavesdrop packer to system. & (1) & Activate/Dissactivate certain functions maliciously. & (1) & Encryption on messages. \\  & Malware codes can modify themselves to look different each time they replicate and deceive the system to download them into system. & (1) & Execute damage. & (1) & Intrusion detection. \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Cyber-attacks on intra-vehicle systems and the defenses. On the other hand, network monitoring and intrusion detection should be implemented on intra-vehicle systems. Typically, attacks on the system last for several minutes or more, therefore, it is essential to monitor the network and to detect possible attacks as soon as possible. For this purpose, real-time intrusion detection and response on the system could be adopted on the system. Currently, most intrusion detection for the system is either based on misuse or based on anomaly detection. Compared the misuse detection, anomaly detection can not only identify specific attacks, but identify some unknown attacks by discovering abnormal frames transmitted on the traffic [91]. To develop intrusion detection for intra-vehicle systems, some issues should be considered. Firstly, the detector should be appropriately deployed in the system. Usually, the detector could be host-based or network-based. Secondly, the detecting methodologies should be carefully considered. The abnormal detection may capture the abnormal patterns according to predefined ones [92], or analyze the unusual frequency or time interval [93]. In the last example, the accuracy of detection matters a lot.