  Connected and autonomous vehicles (CAVs) will form the backbone of future
next-generation intelligent transportation systems (ITS) providing travel
comfort, road safety, along with a number of value-added services. Such a
transformation---which will be fuelled by concomitant advances in technologies
for machine learning (ML) and wireless communications---will enable a future
vehicular ecosystem that is better featured and more efficient. However, there
are lurking security problems related to the use of ML in such a critical
setting where an incorrect ML decision may not only be a nuisance but can lead
to loss of precious lives. In this paper, we present an in-depth overview of
the various challenges associated with the application of ML in vehicular
networks. In addition, we formulate the ML pipeline of CAVs and present various
potential security issues associated with the adoption of ML methods. In
particular, we focus on the perspective of adversarial ML attacks on CAVs and
outline a solution to defend against adversarial attacks in multiple settings.
