Abstract
The components and systems involved in railway operation are subject to stringent reliability and safety requirements, but up until now the cyber security of those same systems has been largely under-explored. In this work, we examine a widely-used railway technology, track beacons or balises, which provide a train with its position on the track and often assist with accurate stopping at stations. Balises have been identified as one potential weak link in train signalling systems. We evaluate an automatic train stop controller that is used in real deployment and show that attackers who can compromise the availability or integrity of the balises' data can cause the trains to stop dozens of meters away from the right position, disrupting train service. To address this risk, we have developed a novel countermeasure that ensures the correct stopping of the trains in the presence of attacks, with only a small extra stopping delay.