  Cross-chain bridges are solutions that enable interoperability between
heterogeneous blockchains. In contrast to the underlying blockchains, the
bridges often provide inferior security guarantees and have been targets of
hacks causing damage in the range of 1.5 to 2 billion USD in 2022. The current
state of bridge architectures is that they are ambiguous, and there is next to
no notion of how different architectures and their components are related to
different vulnerabilities. Throughout this study, we have analysed 60 different
bridges and 34 bridge exploits in the last three years (2021-2023). Our
analyses identified 13 architectural components of the bridges. We linked the
components to eight types of vulnerabilities, also called design flaws. We
identified prevention measures and proposed 11 impact reduction measures based
on the existing and possible countermeasures to address the imminent exploits
of the design flaws. The results are meant to be used as guidelines for
designing and implementing secure cross-chain bridge architectures, preventing
design flaws, and mitigating the negative impacts of exploits.
