  Validators in permissionless, large-scale blockchains (e.g., Ethereum) are
typically payoff-maximizing, rational actors. Ethereum relies on in-protocol
incentives, like rewards for validators delivering correct and timely votes, to
induce honest behavior and secure the blockchain. However, external incentives,
such as the block proposer's opportunity to capture maximal extractable value
(MEV), may tempt validators to deviate from honest protocol participation.
  We show a series of commitment attacks on LMD GHOST, a core part of
Ethereum's consensus mechanism. We demonstrate how a single adversarial block
proposer can orchestrate long-range chain reorganizations by manipulating
Ethereum's reward system for timely votes. These attacks disrupt the intended
balance of power between proposers and voters: by leveraging credible threats,
the adversarial proposer can coerce voters from previous slots into supporting
blocks that conflict with the honest chain, enabling a chain reorganization at
no cost to the adversary. In response, we introduce a novel reward mechanism
that restores the voters' role as a check against proposer power. Our proposed
mitigation is fairer and more decentralized -- not only in the context of these
attacks -- but also practical for implementation in Ethereum.
