Ethereum Faces 25% Drop in Validator Participation After Fusaka Upgrade

Ethereum sees 25% validation drop post-Fusaka as Prysm bug nears finality loss

Following the recent Fusaka upgrade, the Ethereum network experienced a significant decline in validator participation. This drop was largely attributed to a bug in the Prysm consensus client, which caused a notable portion of votes to go offline.

According to an announcement from Prysm on Thursday, the new version v7.0.0 of their client incorrectly generated outdated states while processing older attestations. Prysm's core developer, Terence Tsao, indicated that this flaw disrupted the normal functioning of the nodes. As a temporary fix, developers suggested users start the client using the “--disable-last-epoch-targets” command.

Data from Beaconcha.in shows that during epoch 411,448, the Ethereum network only reached 75% sync participation—referring to the percentage of 512 randomly selected nodes that signed chain heads—and 74.7% voting participation. This 25% drop in voting participation is dangerously close to the network's loss of the two-thirds supermajority required for maintaining finality and regular operations.

As of now, the current Ethereum epoch (411,712) has nearly bounced back, boasting roughly 99% voting participation and reaching 97% sync participation—an improvement indicating network recovery. In the lead-up to these issues, epochs typically enjoyed voting participation rates exceeding 99%.

The decrease in voting participation aligns with the proportion of validators using the Prysm consensus client, which was estimated at 22.71% on Wednesday but dropped to 18% following the incident, suggesting that the attestation failures were mainly affecting Prysm validators.

Client diversity chart. Source: MigaLabs

Neither the Ethereum Foundation nor Prysm developer organization Offchain Labs responded to Cointelegraph's request for comment by the time of publication.

Key Takeaways:

Ethereum experienced a 25% decline in validator voting participation post-Fusaka upgrade due to a bug in the Prysm client.
Only 75% sync participation was recorded during epoch 411,448, with a temporary fix recommended for users.
Current data shows that voting participation is recovering, nearing 99% in the latest epoch.
The incident demonstrated risks associated with insufficient client diversity, as over half of the consensus nodes still rely on a single client, Lighthouse.

Concerns About Finality Loss

If voting participation falls below two-thirds of the total staked Ether, the Ethereum network risks losing finality. In such a scenario, while blocks can still be produced, the chain would no longer be regarded as finalized.

This vulnerability could lead to substantial risks: layer-2 bridges may freeze, rollups would halt withdrawals, and exchanges might raise their block confirmation requirements due to possible chain reorganization during heightened risk periods.

The threat of losing finality is not just hypothetical. In early May 2023, Ethereum's mainnet faced finality loss—an event that occurred twice within a 24-hour period, caused by bugs in handling older attestations in both the Prysm and Teku consensus clients.

Developers had estimated that Prysm was operational on over two-thirds of consensus nodes back in September 2021, further emphasizing the severe consequences that could arise from such outages.

Client diversity chart. Source: Michael Sproul

The Need for Greater Client Diversity

Despite some improvements in Ethereum's consensus client diversity since 2022, it remains critically low, facing challenges in ensuring no single client can disrupt network finality. Current data from MigaLabs indicates that Lighthouse comprises 52.55% of the consensus nodes, while Prysm follows at 18%.

Client diversity chart. Source: MigaLabs

This situation marks a regression from prior to the incident when Lighthouse had below 48.5% and Prysm was around 22.71%, according to MigaLabs. Ethereum educator Anthony Sassano pointed out in an X post that if Lighthouse had experienced the bug instead, the network would have suffered a loss of finalization.

Related: Exclusive data from EigenPhi reveals that sandwich attacks on Ethereum have waned