Sequencer bug stops Coinbase’s Base in two outages

Coinbase’s Base network stopped producing new layer-2 blocks on two consecutive days last week, first for 116 minutes and then for 20 minutes. Sequencing and validator nodes could not advance past an invalid block during each incident.

A post-mortem traced the outages to a bug in the sequencer’s block-building logic. When an invalid transaction failed during execution, the block builder failed to clear the journal state that recorded accounts and storage slots that had been accessed.

The report stated the block builder ‘erroneously did not clear the journal state that contained the accounts and storage slots that had been accessed.’ Because Base uses a single sequencer to order transactions, that persistent journal state prevented both sequencer and validator nodes from progressing until sequencing was restored.

Engineers applied a patch to ensure the journal state is properly updated during execution, which restored block production. Mitigation took longer than expected due to infrastructure conditions unrelated to the original bug, and a race condition after a system reset prevented sequencers from catching up and contributed to the second outage.

The post-mortem said engineers will increase protocol fuzz testing-sending random or malformed inputs to find flaws-and add graceful recovery so validator nodes do not require manual restarts. The report also identified the post-reset race condition as an immediate area for attention.

Base experienced prior sequencer-related stoppages, including a 17-minute outage in September 2024 and an about 30-minute outage in August 2025. The network secures just under $11 billion in total value.