In industrial control systems, devices such as Programmable Logic Controllers (PLCs) are commonly used to directly interact with sensors and actuators, and perform local automatic control. PLCs run software on two different layers: a) firmware (i.e. the OS) and b) control logic (processing sensor readings to determine control actions). In this work, we discuss ladder logic bombs, i.e. malware written in ladder logic (or one of the other IEC 61131-3-compatible languages). Such malware would be inserted by an attacker into existing control logic on a PLC, and either persistently change the behavior, or wait for specific trigger signals to activate malicious behaviour. For example, the LLB could replace legitimate sensor readings with manipulated values. We see the concept of LLBs as a generalization of attacks such as the Stuxnet attack. We introduce LLBs on an abstract level, and then demonstrate several designs based on real PLC devices in our lab. In particular, we also focus on stealthy LLBs, i.e. LLBs that are hard to detect by human operators manually validating the program running in PLCs. In addition to introducing vulnerabilities on the logic layer, we also discuss countermeasures and we propose two detection techniques.
@cite_22 Morris discuss different attacks such as measurement injection, command injection, denial of service, etc, on SCADA control systems which use the MODBUS communication protocol. Much like the rest, this study is again restricted to exploiting the network layer to attack the PLCs. Therefore, it is necessary to analyze control logic vulnerabilities, which can be manifested through malicious logic additions.
@cite_22
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This paper presents a set of attacks against SCADA control systems. The attacks are grouped into 4 classes; reconnaissance, response and measurement injection, command injection and denial of service. The 4 classes are defined and each attack is described in detail. The response and measurement injection and command injection classes are subdivided into sub-classes based on attack complexity. Each attack described in this paper has been exercised against industrial control systems in a laboratory setting. SCADA systems are widely used in critical infrastructure sectors, including electricity generation and distribution, oil and gas production and distribution, and water treatment and distribution. SCADA process control systems are typically isolated from the internet via firewalls. However, they may still be subject to illicit cyber penetrations and may be subject to cyber threats from disgruntled insiders. We have developed a set of command injection, data injection, and denial of service attacks which leverage the lack of authentication in many common control system communication protocols including MODBUS, DNP3, and EtherNET IP. We used these exploits to aid in development of a neural network based intrusion detection system which monitors control system physical behavior to detect artifacts of command and response injection attacks. Finally, we present intrusion detection accuracy results for our neural network based IDS which includes input features derived from physical properties of the control system. An experimental investigation was undertaken to understand the impact of single-point cyber attacks on a Secure Water Treatment (SWaT) system. Cyber attacks were launched on SWaT through its SCADA server that connects to the Programmable Logic Controllers (PLCs) that in turn are connected to sensors and actuators. Attacks were designed to meet attacker objectives selected from a novel attacker model. Outcome of the experiments led to a better understanding of (a) the propagation of an attack across the system measured in terms of the number of components affected and (b) the behavior of the water treatment process in SWaT in response to the attacks. The observed response to various attacks was then used to propose attack detection mechanisms based on various physical properties measured during the treatment process. In the last years there has been an increasing interest in the security of process control and SCADA systems. Furthermore, recent computer attacks such as the Stuxnet worm, have shown there are parties with the motivation and resources to effectively attack control systems. While previous work has proposed new security mechanisms for control systems, few of them have explored new and fundamentally different research problems for securing control systems when compared to securing traditional information technology (IT) systems. In particular, the sophistication of new malware attacking control systems--malware including zero-days attacks, rootkits created for control systems, and software signed by trusted certificate authorities--has shown that it is very difficult to prevent and detect these attacks based solely on IT system information. In this paper we show how, by incorporating knowledge of the physical system under control, we are able to detect computer attacks that change the behavior of the targeted control system. By using knowledge of the physical system we are able to focus on the final objective of the attack, and not on the particular mechanisms of how vulnerabilities are exploited, and how the attack is hidden. We analyze the security and safety of our mechanisms by exploring the effects of stealthy attacks, and by ensuring that automatic attack-response mechanisms will not drive the system to an unsafe state. A secondary goal of this paper is to initiate the discussion between control and security practitioners--two areas that have had little interaction in the past. We believe that control engineers can leverage security engineering to design--based on a combination of their best practices--control algorithms that go beyond safety and fault tolerance, and include considerations to survive targeted attacks.