Methodology for Assessing Existing Vulnerabilities in Modbus Protocol

Modbus protocol is one of the most extensively used communication protocols in Industrial Control Systems (ICS) because of its simplicity reliability, and basic position in ICS communication and availability as an open-source solution, However, the rising use of Ethernet Modbus TCP/IP connections and their integration with the internet have exposed this protocol to a variety of security concerns. A comprehensive assessment of related literature shows that the lack of encryption is a fundamental flaw in the Modbus protocol used in ICS systems. In this study, we evaluate the vulnerability of Modbus communication configuration by providing the methodology for assessing the existing vulnerability: Lack of Encryption, which includes an Allen-Bradley (1769-L30ER) Programmable Logic Controller (PLC) as the server and a Modbus Poll client (PC). The results revealed clearly that the sent data remained in plain text, making it vulnerable to interception and modification. In addition, we performed a Denial-of-Service (DoS) attack on the experimental setup to demonstrate how easily inside attackers may exploit this existing vulnerability. As a result, improving the security of the Modbus protocol is essential. This study attempts to throw attention on the critical need to improve Modbus protocol security mechanisms in order to protect ICS systems from possible attacks.