Cyber-Physical Systems (CPS) often involve complex networks of interconnected software and hardware components that are logically combined to achieve a common goal or mission; for example, keeping a plane in the air or providing energy to a city. Failures in these components may jeopardise the mission of the system. Therefore, identifying the minimal set of critical CPS components that is most likely to fail, and prevent the global system from accomplishing its mission, becomes essential to ensure reliability. In this article, we present a novel approach to identifying the Most Likely Mission-critical Component Set (MLMCS) using AND/OR dependency graphs enriched with independent failure probabilities. We address the MLMCS problem as a Maximum Satisfiability (MaxSAT) problem. We translate probabilities into a negative logarithmic space to linearise the problem within MaxSAT. The experimental results conducted with our open source tool LDA4CPS indicate that the approach is both effective and efficient. We also present a case study on complex aircraft systems that shows the feasibility of our approach and its applicability to mission-critical cyber-physical systems. Finally, we present two MLMCS-based security applications focused on system hardening and forensic investigations.

a b s t r a c tIn recent years, Industrial Control Systems (ICS) have become increasingly exposed to a wide range of cyber-physical attacks, having massive destructive consequences.Security metrics are therefore essential to assess and improve their security posture.In this paper, we present a novel ICS security metric based on AND/OR graphs and hypergraphs which is able to efficiently identify the set of critical ICS components and security measures that should be compromised, with minimum cost (effort) f or an attacker, in order to disrupt the operation of vital ICS assets.Our tool, META4ICS (pronounced as metaphorics ), leverages state-of-the-art methods from the field of logical satisfiability optimisation and MAX-SAT techniques in order to achieve efficient computation times.In addition, we present a case study where we have used our system to analyse the security posture of a realistic Water Transport Network (WTN).

Attack graphs are a powerful tool for security risk assessment by analysing network vulnerabilities and the paths attackers can use to compromise network resources. The uncertainty about the attacker's behaviour makes Bayesian networks suitable to model attack graphs to perform static and dynamic analysis. Previous approaches have focused on the formalization of attack graphs into a Bayesian model rather than proposing mechanisms for their analysis. In this paper we propose to use efficient algorithms to make exact inference in Bayesian attack graphs, enabling the static and dynamic network risk assessments. To support the validity of our approach we have performed an extensive experimental evaluation on synthetic Bayesian attack graphs with different topologies, showing the computational advantages in terms of time and memory use of the proposed techniques when compared to existing approaches.

Monitoring systems are essential to understand and control the behaviour of systems and networks. Cyber-physical systems (CPS) are particularly delicate under that perspective since they involve real-time constraints and physical phenomena that are not usually considered in common IT solutions. Therefore, there is a need for publicly available monitoring tools able to contemplate these aspects. In this poster/demo, we present our initiative, called CPS-MT, towards a versatile, real-time CPS monitoring tool, with a particular focus on security research. We first present its architecture and main components, followed by a MiniCPS-based case study. We also describe a performance analysis and preliminary results. During the demo, we will discuss CPS-MT's capabilities and limitations for security applications.

In this paper, we describe an efficient methodology to guide investigators during network forensic analysis. To this end, we introduce the concept of core attack graph, a compact representation of the main routes an attacker can take towards specific network targets. Such compactness allows forensic investigators to focus their efforts on critical nodes that are more likely to be part of attack paths, thus reducing the overall number of nodes (devices, network privileges) that need to be examined. Nevertheless, core graphs also allow investigators to hierarchically explore the graph in order to retrieve different levels of summarised information. We have evaluated our approach over different network topologies varying parameters such as network size, density, and forensic evaluation threshold. Our results demonstrate that we can achieve the same level of accuracy provided by standard logical attack graphs while significantly reducing the exploration rate of the network.

Computer and network systems are consistently exposed to security threats, making their management even more complex. The management of known vulnerabilities plays a crucial role for ensuring their safe configurations and preventing security attacks. However, this activity should not generate new vulnerable states. In this paper we present a novel approach for autonomously assessing and remediating vulnerabilities. We describe a detailed mathematical model that supports this activity and we formalize the remediation decision process as a SAT problem. We present a framework that is able to assess OVAL vulnerability descriptions and perform corrective actions by using XCCDF-based descriptions of future machine states and the NETCONF protocol. We also provide details of our implementation and evaluate its feasibility through a comprehensive set of experiments.

The development of mobile technologies and services has contributed to the large-scale deployment of smartphones and tablets. These environments are exposed to a wide range of security attacks and may contain critical information about users such as contact directories and phone calls. Assessing configuration vulnerabilities is a key challenge for maintaining their security, but this activity should be performed in a lightweight manner in order to minimize the impact on their scarce resources. In this paper we present a novel approach for assessing configuration vulnerabilities in mobile devices by using a probabilistic cost-efficient security framework. We put forward a probabilistic assessment strategy supported by a mathematical model and detail our assessment framework based on OVAL vulnerability descriptions. We also describe an implementation prototype and evaluate its feasibility through a comprehensive set of experiments.

Vulnerability management constitutes a crucial activity within autonomic networks and systems. Distributed vulnerabilities must be assessed over a consolidated view of the network in order to detect vulnerable states that may simultaneously involve two or more devices. In this work, we present a novel approach for describing and assessing distributed vulnerabilities in such self-governed environments. We put forward a mathematical construction for defining distributed vulnerabilities as well as an extension of the OVAL language called DOVAL for describing them. We then define a framework for assessing distributed vulnerabilities in autonomic environments that exploits the knowledge provided by such descriptions. We finally show the feasibility of our solution by analyzing the behavior of the proposed algorithms and strategies through a comprehensive set of experiments.

The nature of computer crimes has systematically evolved with the progress of computer technologies. Due to the complexity of forensic investigations, the design of new techniques and tools for speeding up and automating tasks required by digital forensic processes has become a challenging task. In particular, the collection of (live) digital evidence is a delicate work that requires special care and proved investigator skills. This work presents a framework for the specification of collection procedures based on an extension of the OVAL language and describes a tool that has been implemented to automate the execution of those procedures.