  In May 2023, the Ethereum blockchain experienced its first inactivity leak, a
mechanism designed to reinstate chain finalization amid persistent network
disruptions. This mechanism aims to reduce the voting power of validators who
are unreachable within the network, reallocating this power to active
validators. This paper investigates the implications of the inactivity leak on
safety within the Ethereum blockchain. Our theoretical analysis reveals
scenarios where actions by Byzantine validators expedite the finalization of
two conflicting branches, and instances where Byzantine validators reach a
voting power exceeding the critical safety threshold of one-third.
Additionally, we revisit the probabilistic bouncing attack, illustrating how
the inactivity leak can result in a probabilistic breach of safety, potentially
allowing Byzantine validators to exceed the one-third safety threshold. Our
findings uncover how penalizing inactive nodes can compromise blockchain
properties, particularly in the presence of Byzantine validators capable of
coordinating actions.
