Base Post-Incident Review of the Network Outage: User Funds Were Not Affected; the Vulnerability Stemmed from the Sequencer Block Construction Logic

Shenchao TechFlow News: On June 27, the Base engineering team released a postmortem report on the block production outage that occurred on June 25.

The report shows that the Base mainnet experienced two block production outages on June 25 at 11:47 AM and on June 26 at 11:28 AM (Eastern Time). The outages lasted 116 minutes and 20 minutes, respectively. Officially, the two incidents were caused by the same technical issue. The chain’s integrity was not affected, and user funds remained safe at all times.

Based on the investigation, the root cause was a vulnerability in the block construction logic of the sequencer. When a transaction validation failed, the system was unable to properly clear the expired log state information.

Specifically, after an invalid transaction was received by the block builder and failed to execute as expected, the system incorrectly retained the account and storage slot access records involved in it. Subsequently, another valid transaction executed without clearing the relevant state, leading to inconsistent gas accounting results and ultimately generating a sequenced block containing an invalid state transition.

Because other nodes could not verify and accept this block, the network consensus process was blocked, causing on-chain block production to come to a complete halt.

During the incident, Base was unable to produce new Layer2 blocks. Neither the sequencer nor the validator nodes could bypass the invalid block to continue, and users’ newly submitted transactions also could not be completed on-chain.

The Base team then restored normal network operations by deploying a patch to the sequencer to ensure that the log state during execution could be correctly updated.

Officially, they stated that going forward, they will further strengthen protocol fuzz testing and stress testing capabilities to detect potential vulnerabilities triggered by similar adversarial transaction patterns earlier. Meanwhile, the team will continue optimizing operational processes and monitoring systems to improve network stability and incident response capabilities.