Base blames same sequencer bug for two-day outage, says user funds were safe
Coinbase-backed layer-2 network Base says a single bug in its sequencer block-building logic caused its mainnet to stop producing blocks twice over June 25–26. The two outages — about 116 minutes on June 25 and roughly 20 minutes on June 26 — prevented new transactions from being included onchain, but Base emphasized that “the integrity of the chain was not compromised and all funds on Base were safe.”
What happened
- During block execution a transaction failed as expected, but stale journal state from that failure remained inside the block builder.
- When the next (valid) transaction executed, the system used the wrong journal state and charged gas incorrectly, producing a block with an invalid state transition.
- Other nodes rejected that invalid block, halting block production across the L2 until sequencing recovered.
User impact and operational effects
- While sequencing was halted, transactions queued in the mempool; the pool later grew beyond capacity, causing eth_sendRawTransaction requests to return errors during the outage window.
- Sequencer and validator progress were affected because nodes could not advance past the invalid block until sequencing resumed. Base says sequencers were primarily impacted by the second recovery issue rather than validator nodes.
How Base fixed it
- Engineers applied a sequencer patch that forces proper journal-state updates after a failed transaction, addressing the root cause.
- During recovery they discovered a second problem: a race condition in the engine reset feature that impeded sequencers from catching up after restart. That helped explain the recurrence on June 26 and made mitigation slower.
- Base advised node operators to restart nodes if they remained stuck; block production resumed after mitigation.
What Base will do next
- The team has published a postmortem and shared feedback with OP chains. It intends to strengthen protocol fuzz testing and load testing to expose edge-case transaction patterns.
- Base will add better monitoring and operational checks to detect similar issues earlier and respond faster.
- It also plans to add graceful recovery to base-consensus so validator nodes can continue syncing more easily after comparable failures.
Context
The outage coincided with a busy week for Base, which pushed forward with its Beryl upgrade (introducing the B20 token standard and shortening Base-to-Ethereum withdrawals from seven to five days). Base says it has now named the bug, released a patch, and outlined testing improvements to reduce the risk of a repeat.
Bottom line
The incident exposed a sequencer-level edge case that stopped block production but did not put user funds at risk. Base has fixed the immediate failure, identified a follow-up race condition, and laid out testing and monitoring upgrades to strengthen resilience going forward.
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