Shortly after the Fusaka network upgrade, the Ethereum network saw a sharp drop in validator participation after a bug in the Prysm consensus client knocked a chunk of votes offline.
According to a Thursday Prysm announcement, version v7.0.0 of the client unnecessarily generated old states while processing outdated attestations, a flaw that Prysm core developer Terence Tsao said prevented the nodes from functioning correctly. Developers recommended that users launch the client with the โ–disable-last-epoch-targetsโ flag as a temporary workaround.
Beaconcha.in network data shows that at epoch 411,448, the network achieved only 75% sync participation (the percentage of 512 randomly selected nodes signing chain heads) and 74.7% voting participation. Voting participation being down 25% is under 9% shy of the network losing the two-thirds supermajority needed to maintain finality and regular operation.
At the time of writing, the current Ethereum network epoch (411,712) is experiencing nearly 99% voting participation and has reached 97% sync participation, indicating that the network has recovered. Prior to the issue, epochs routinely saw well over 99% of vote participation.
The decline in vote participation roughly matches the share of validators using the Prysm consensus client, estimated at 22.71% on Wednesday, before falling to 18% after the incident. This suggests that the attestation failure was likely concentrated among Prysm validators.
The Ethereum Foundation and Prysm developer organization Offchain Labs had not answered Cointelegraphโs request for comment by publication.
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Brushing with finality loss
If voting participation falls below two-thirds of the total staked Ether (ETH), the Ethereum network loses finality. Under Ethereumโs design, blocks can still be produced in that scenario, but the chain is no longer considered finalized.
As a likely consequence of such an outage, layer-2 bridges would freeze, rollups would pause withdrawals, and exchanges would increase their block confirmation requirements amid heightened risk of chain reorganization.
A similar incident that could lead to Ethereum losing finality is not purely theoretical. In early May 2023, the Ethereum mainnet lost finality โ an incident that occurred twice within 24 hours due to bugs in the handling of old-target attestations in the Prysm and Teku consensus clients.
The incident could have led to much worse consequences, since Prysm was estimated by its developers to run on over two-thirds of the consensus nodes back in September 2021. Data shared in January 2022 by Michael Sproul, a developer working on the current majority consensus client, Lighthouse, showed that Prysm was running on 68.1% of nodes.
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Client diversity is still insufficient
While Ethereum consensus client diversity has made some progress since 2022, it is still far from achieving a client count under 33%, a limit that would ensure that a bug in a single client is not enough to halt network finality. Current MigaLabs data indicates that Lighthouse alone accounts for 52.55% of consensus nodes, with Prysm in second place at 18%.
That represents a deterioration from before the incident, when Lighthouse was below 48.5% and Prysm around 22.71%, according to MigaLabs.
Ethereum educator Anthony Sassano noted in an X post that โif Lighthouse had had the bug instead, then the network wouldโve lost finalization.โ
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