Don't Trust, Verify: The Case of Slashing from a Popular Ethereum Explorer

Blockchain explorers are important tools for quick look-ups of on-chain activities. However, as centralized data providers, their reliability remains under-studied. As a case study, we investigate Beaconcha.in, a leading explorer serving Ethereum's proof-of-stake (PoS) update. According to the explorer, we find that more than 75% of slashable Byzantine actions were not slashed. Since Ethereum relies on the "stake-and-slash" mechanism to align incentives, this finding would at its face value cause concern over Ethereum's security. However, further investigation reveals that all the apparent unslashed incidents were erroneously recorded due to the explorer's mishandling of consensus edge cases. Besides the usual message of using caution with centralized information providers, our findings also call for attention to improving the monitoring of blockchain systems that support high-value applications.