Vitalik responds to the "Prysm client" vulnerability incident: Ethereum occasionally lacks finality, and that's okay! Just avoid finalization errors.

Ethereum co-founder Vitalik Buterin personally addressed the recent Prysm client vulnerability that nearly caused finality loss, downplaying community concerns: “Occasional loss of finality is completely fine. What really matters is not finalizing the wrong block.” He emphasized that a delay of a few hours has no significant impact, and the chain can still operate normally. The key red line is only one thing: never finalize the wrong block. (Background summary: Quick overview: What benefits does the Fusaka upgrade bring to Ethereum?) (Additional background: Vitalik’s call: Ethereum’s gas limit to increase fivefold again by 2026, but inefficiency will be penalized fivefold!) Shortly after the Ethereum mainnet completed the Fusaka upgrade on December 3, the Prysm client (approximately 23% market share) experienced a vulnerability in version v7.0.0, causing many validators to vote incorrectly. The network’s participation rate once dropped below 75%, just 9 percentage points from losing finality entirely, sparking panic in the community. However, thanks to urgent developer coordination, the issue was fixed within hours, and on-chain finality was successfully restored. Vitalik Buterin personally responded: Occasional loss of finality is no big deal Although the vulnerability was promptly resolved, the community’s discussion was lively. In response, Ethereum co-founder Vitalik Buterin posted on X to calm the public, stating: "I personally think, occasional loss of finality is completely fine. Finality is used when we are really sure that a block will not be reverted. If a major client has a bug causing finality to delay by a few hours, that’s okay. The chain still continues during that time. The thing to avoid is… — vitalik.eth (@VitalikButerin) December 4, 2025 Ethereum protocol expert fully agrees According to Cointelegraph, Fabrizio Romano Genovese, a PhD in computer science from Oxford University, a partner at blockchain research firm 20squares, and an Ethereum protocol expert, expressed 100% agreement with Vitalik’s statement, further explaining: “When Ethereum loses finality, it essentially temporarily degrades into Bitcoin’s mode. Bitcoin has never had definitive finality since its launch in 2009, yet people still use it happily.” He emphasized that losing finality does not mean the chain is insecure, only that the guarantee against reorganization shifts from ‘certainty’ to ‘probability’. In May 2023, due to Prysm and Teku client bugs, Ethereum lost finality twice for a total of 24 hours, but the mainnet continued to produce blocks normally, without systemic risk. Additionally, Genovese pointed out that the real impact would be on Layer 2 solutions and cross-chain bridges that rely heavily on finality. For example, Polygon’s AggLayer might suspend deposits and withdrawals, but user funds will not be rolled back; at worst, transaction confirmation might be slower. He believes that if bridging developers do not implement proper fallback mechanisms for temporary finality loss, it’s a developer responsibility, not a protocol issue. What exactly is Ethereum’s “finality”? Ethereum’s finality (Finality) is a core guarantee of its PoS consensus: when a block receives votes from over 66% (2/3) of validators across the network, it is marked as “justified”; if this state is maintained across two consecutive epochs with over 2/3 votes, the block is “finalized”; once finalized, it is theoretically impossible to revert unless more than 1/3 of validators maliciously act and are willing to have their substantial staked ETH destroyed. If voting participation remains below 66% for an extended period, the “Inactivity Leak” mechanism is activated to penalize offline validators, encouraging the network to recover. Related reports: Why did Vitalik push Kohaku again and donate 256 ETH? Vitalik warns: Smart people need “stupid rules” and should not easily fall into moral reasoning traps. Vitalik signs the “Trustless Declaration,” how account abstraction can rewrite private keys, security, and on-chain experience. <Vitalik responds to Prysm client vulnerability: Occasional loss of Ethereum finality is okay! Just don’t finalize the wrong block> This article was first published on BlockTempo, a leading blockchain news media.