Prysm post-mortem pins Fusaka disruption on costly state recomputation — network dodges finality loss Prysm developers have published a post-mortem explaining the December 4 incident that threatened Ethereum’s stability immediately after the Fusaka upgrade. The problem was traced to resource exhaustion in Prysm: certain attestations triggered expensive recomputation of obsolete historical states, which overwhelmed affected nodes’ CPU and memory and left validators struggling to keep up. The bug appeared the moment Fusaka activated at epoch 411392 (December 4, 2025, 21:49 UTC). Validator participation collapsed from normal levels above 95% to roughly 75%, causing the network to miss 41 epochs and costing validators about 382 ETH in lost rewards. Prysm developers pushed emergency runtime flags to mitigate the issue and shipped permanent fixes in client releases v7.0.1 and v7.1.0. What went wrong Prysm’s core team says the failure centered on how the client handled “historical state.” As Prysm core developer Terence Tsao put it, “historical state is compute memory heavy, a node can be dosed by large number of state replays happening in parallel.” In short, certain attestations forced heavy state replays that consumed resources and produced a denial-of-service condition on Prysm nodes. Scope and risk Validators running Prysm represented an estimated 15% to 22.71% of the network, so the performance collapse of that subset drove the participation drop and pushed Ethereum alarmingly close to losing finality. The post-mortem notes that had the bug hit a different consensus client (for example, Lighthouse) covering a larger share of validation, the network might have lost finality entirely — an event that would likely freeze Layer 2 rollups and block validator withdrawals until fixes were deployed. Why the network survived The incident highlights the value of client diversity. While Prysm validators were impaired, ten other consensus clients — including Lighthouse, Nimbus, and Teku — continued to validate normally. Because roughly 75% to 85% of validators remained operational across other clients, finality was preserved and the chain continued processing transactions. Response and recovery The Ethereum Foundation quickly issued emergency guidance to Prysm operators. Validators applied the temporary mitigations while Prysm engineers developed and released permanent fixes (v7.0.1 and v7.1.0). By December 5, participation rebounded to nearly 99%, and normal operations were restored within 24 hours of the incident. Context: Fusaka and PeerDAS Fusaka itself — which introduced PeerDAS (Peer Data Availability Sampling) to expand blob capacity for Layer 2 scaling by roughly eightfold — executed successfully with zero downtime before the Prysm-specific bug surfaced. The upgrade’s innovations remain intact; the disruption stemmed from a client implementation issue rather than the protocol change. Bottom line The Fusaka incident was a serious, but short-lived, stress test of Ethereum’s resilience. A Prysm implementation bug caused heavy historical-state recomputation and degraded a significant slice of validators, but client diversity and fast remediation prevented catastrophic finality loss. The event underscores both the importance of robust client testing and the practical benefits of a multi-client ecosystem for Ethereum. Read more AI-generated news on: undefined/news

#ETH