| Summary: | Industrial control systems (ICS) are being used for surveillance and controlling numerous industrial process plants in national critical infrastructures. Supervisory control and data acquisition (SCADA) system is a core component in ICS systems for continuous monitoring and controlling these process plants. Legacy SCADA systems are working in isolated networks and using proprietary communication protocols which made them less exposed to cyber threats. In recent times, these ICS systems have been connected to Internet and corporate networks for data sharing and remote monitoring. They are also using open protocols and operating systems. This leads to vulnerabilities of the system to cyberattacks. Cybersecurity threats are more prevalent than ever in ICS systems. These attacks may be external or internal. Modbus is a widely deployed communication protocol for SCADA communications. There is no security in design of Modbus protocol, and it is vulnerable to numerous cyberattacks. In this paper, we worked for False Command Injection attack, False Access Injection attack, and replay attacks on Modbus protocol. Initially, a real-time SCADA testbed was set up, and we envisaged the impact of these attacks on Modbus protocol data using the testbed. In this work, we used local area network (LAN) environment only for simulating the attacks. We assumed that the attacks penetrated the LAN network. We proposed and developed (a) a method to detect replay attacks by incorporating time stamp and sequence number in Modbus communications and (b) a frame filtering module which will block unauthorized attacks like False Command Injection and False Access Injection attacks to reach programmable logic controller (PLC). Numbers of attacks were simulated and the performance of the method was measured using attack block rate (ABR). It blocked 97% of malicious Modbus transactions or attacks to reach the PLC. It protects SCADA systems from attackers, which is a core component of industrial control systems. The solution enhanced the security of SCADA systems with Modbus protocol.
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