Optimal Security Response to Network Intrusions in IT Systems

Academic Dissertation which, with due permission of the KTH Royal Institute of Technology, is submitted for public defence for the Degree of Doctor of Philosophy on Thursday the 5th December 2024, at 14:00 in F3, Lindstedtsvägen 26, Stockholm.

The defense will be streamed via Zoom: https://kth-se.zoom.us/j/64592772191

Candidate: Kim Hammar

Supervisor: Professor Rolf Stadler, KTH, Sweden

Opponent: Professor Tansu Alpcan, The University of Melbourne, Australia

Grading committee:

 - Professor Emil Lupu, Imperial College London, UK

 - Professor Alina Oprea, Northeastern University, USA

 - Professor Karl H. Johansson, KTH, Sweden

Reviewer: Professor Henrik Sandberg, KTH, Sweden

QC 20241111

Abstract

Cybersecurity is one of the most pressing technological challenges of our time and requires measures from all sectors of society. A key measure is automated security response, which enables automated mitigation and recovery from cyber attacks. Significant strides toward such automation have been made due to the development of rule-based response systems. However, these systems have a critical drawback: they depend on domain experts to configure the rules, a process that is both error-prone and inefficient. Framing security response as an optimal control problem shows promise in addressing this limitation but introduces new challenges. Chief among them is bridging the gap between theoretical optimality and operational performance. Current response systems with theoretical optimality guarantees have only been validated analytically or in simulation, leaving their practical utility unproven.

This thesis tackles the aforementioned challenges by developing a practical methodology for optimal security response in IT infrastructures. It encompasses two systems. First, it includes an emulation system that replicates key components of the target infrastructure. We use this system to gather measurements and logs, based on which we identify a game-theoretic model. Second, it includes a simulation system where game-theoretic response strategies are optimized through stochastic approximation to meet a given objective, such as quickly mitigating potential attacks while maintaining operational services. These strategies are then evaluated and refined in the emulation system to close the gap between theoretical and operational performance.

We present CSLE, an open-source platform that implements our methodology. This platform allows us to experimentally validate the methodology on several instances of the security response problem, including intrusion prevention, intrusion response, intrusion tolerance, and defense against advanced persistent threats. We prove structural properties of optimal response strategies and derive efficient algorithms for computing them. This enables us to solve a previously unsolved problem: demonstrating optimal security response against network intrusions on an IT infrastructure.

urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-356193