Shortly following the Fusaka network upgrade, the Ethereum network experienced a significant decline in validator participation due to a bug in the Prysm consensus client that temporarily disrupted a portion of votes.
As per a Prysm announcement on Thursday, version v7.0.0 of the client inappropriately generated outdated states while processing stale attestations, a flaw described by Prysm core developer Terence Tsao as causing nodes to malfunction. Developers advised users to launch the client with the “–disable-last-epoch-targets” flag as a temporary solution.
Beaconcha.in network data indicates that at epoch 411,448, the network recorded only 75% sync participation (the percentage of 512 randomly chosen nodes signing chain heads) and 74.7% voting participation. A 25% decrease in voting participation places the network almost 9% away from losing the two-thirds supermajority necessary for maintaining finality and smooth operation.
As of this writing, the current Ethereum network epoch (411,712) is enjoying close to 99% voting participation and has reached 97% sync participation, suggesting that the network has rebounded. Before the issue arose, epochs typically experienced participation rates above 99%.
The drop in voting participation aligns closely with the proportion of validators utilizing the Prysm consensus client, estimated at 22.71% on Wednesday, dropping to 18% post-incident. This implies that the attestation failure was predominantly among Prysm validators.
The Ethereum Foundation and Prysm developer organization Offchain Labs had not responded to Cointelegraph’s request for comment by the time of publication.
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Brushing with finality loss
Should voting participation dip below two-thirds of the total staked Ether (ETH), the Ethereum network loses finality. Within Ethereum’s framework, blocks can still be generated in that scenario; however, the chain ceases to be recognized as finalized.
A potential consequence of such an outage would be the freezing of layer-2 bridges, the pausing of rollup withdrawals, and exchanges raising their block confirmation requirements due to increased risk of chain reorganization.
A comparable event that could jeopardize Ethereum’s finality is not merely hypothetical. In early May 2023, the Ethereum mainnet lost finality — an occurrence that happened twice within 24 hours due to bugs in the handling of old-target attestations in the Prysm and Teku consensus clients.
This incident could have resulted in more severe repercussions since Prysm was reported by its developers to operate on over two-thirds of the consensus nodes as of September 2021. Data provided in January 2022 by Michael Sproul, a developer currently working on the majority consensus client, Lighthouse, indicated that Prysm was running on 68.1% of nodes.
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Client diversity remains inadequate
While there has been some improvement in Ethereum consensus client diversity since 2022, it is still far from reaching a client distribution below 33%, a threshold that would prevent a single client bug from disrupting network finality. Current MigaLabs data shows that Lighthouse alone commands 52.55% of consensus nodes, with Prysm trailing at 18%.
This signifies a deterioration from prior to 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 “had Lighthouse been affected by the bug instead, the network would have lost finalization.”
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