Prysm Team Releases Post-Mortem Report on Prysm Beacon Node Resource Exhaustion Incident During Fusaka Upgrade

December 14: The Prysm team published a post-incident review report detailing that on December 4—during Ethereum mainnet’s Fusaka period—nearly all Prysm validator nodes experienced resource exhaustion while processing specific attestations. This led to delayed responses to validator requests and a large number of missed blocks and attestations. The incident impacted 42 epochs (spanning epoch 411439 to 411480), with 248 missed blocks out of 1344 total slots—an approximate 18.5% miss rate. Network participation briefly dropped to 75%, and validators lost roughly 382 ETH in attestation rewards. The root cause was Prysm receiving attestations from potentially out-of-sync mainnet nodes that referenced the block root of the prior epoch. To verify these attestations’ legitimacy, Prysm repeatedly replayed historical epoch states and executed resource-intensive epoch transitions, which caused resource exhaustion under high concurrency. The Prysm team deployed a temporary fix by enabling the `--disable-last-epoch-target` flag in version 7.0.0. Subsequent releases (7.0.1 and 7.1.0) include a permanent fix that validates attestations using the head state, eliminating the need to replay historical states.