Outage Overview: Two Block Production Interruptions
Between June 25 and 26, the Base mainnet — a Layer 2 network incubated by Coinbase — suffered two separate block production outages. According to the post-mortem published by Base engineering on June 27, the first incident occurred at 11:47 AM ET on June 25 and lasted 116 minutes; the second began at 11:28 AM ET on June 26 and lasted 20 minutes. Both outages shared the same root cause, and the chain’s integrity and all user funds remained secure throughout the events.
Root Cause and Remediation
The investigation revealed that the root cause was a vulnerability in the sequencer’s block building logic. When a transaction failed validation, the system did not properly clear its stale log state (which includes accessed accounts and storage slots). As a result, a subsequent valid transaction was executed against the uncleared log state, causing a mismatch in gas accounting. This produced a sequenced block containing an invalid state transition, which other nodes could not accept, bringing the chain to a complete halt. During the incident, Base was unable to produce new L2 blocks, and both the sequencer and validator nodes were stuck, preventing new transactions from being posted on-chain. The team deployed a patch to ensure the log state is correctly updated during execution, thus fixing the bug. Going forward, Base will strengthen its protocol fuzz testing and load testing tools to better identify adversarial transaction patterns that could expose similar vulnerabilities, and will continue to improve operational and monitoring capabilities.