Following the Fusaka network upgrade, the Ethereum network experienced a notable drop in validator participation due to a bug in the Prysm consensus client, which caused a portion of votes to go offline.
As stated in a Thursday Prysm announcement, version v7.0.0 of the client improperly generated old states while managing outdated attestations, a flaw that Prysm core developer Terence Tsao noted prevented nodes from functioning properly. Developers advised users to launch the client with the “–disable-last-epoch-targets” flag as a temporary fix.
Beaconcha.in network data reveals that at epoch 411,448, the network recorded only 75% sync participation (the proportion of 512 randomly selected nodes signing chain heads) and 74.7% voting participation. A 25% drop in voting participation is nearly 9% away from the network losing the two-thirds supermajority essential for maintaining finality and regular function.
As of this writing, the current Ethereum network epoch (411,712) is exhibiting close to 99% voting participation and has achieved 97% sync participation, suggesting that the network has rebounded. Before the issue, epochs commonly recorded well above 99% of voting participation.
The drop in vote participation closely corresponds to the proportion of validators utilizing the Prysm consensus client, estimated at 22.71% on Wednesday, before falling to 18% post-incident. This indicates that the attestation failure was likely concentrated among Prysm validators.
The Ethereum Foundation and the 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
If voting participation dips below two-thirds of the total staked Ether (ETH), the Ethereum network risks losing finality. In Ethereum’s current structure, blocks can still be produced in this situation, but the chain is no longer seen as finalized.
Such an outage could lead to significant issues: layer-2 bridges could freeze, rollups might halt withdrawals, and exchanges could heighten their block confirmation requirements amid increased risk of chain reorganization.
A similar event resulting in Ethereum losing finality is not merely theoretical. In early May 2023, the Ethereum mainnet did lose finality—a situation which occurred twice within 24 hours due to bugs in managing old-target attestations in the Prysm and Teku consensus clients.
The repercussions could have been even more severe, as Prysm was estimated by its developers to operate on over two-thirds of consensus nodes back in September 2021. Data shared in January 2022 by Michael Sproul, a developer involved with the current dominant consensus client, Lighthouse, indicated that Prysm was active on 68.1% of nodes.
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Client diversity is still insufficient
Although there has been some improvement in Ethereum consensus client diversity since 2022, it remains inadequate to ensure that no single client can halt network finality. Current MigaLabs data indicates that Lighthouse alone comprises 52.55% of consensus nodes, with Prysm following at 18%.
This represents a decline from before the incident, when Lighthouse was below 48.5% and Prysm around 22.71%, according to MigaLabs.
Ethereum educator Anthony Sassano pointed out in an X post that “if Lighthouse had had the bug instead, then the network would’ve lost finalization.”
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