Base Post-Mortem: Network Outage Event - User Funds Security at Risk, Root Cause Linked to Vulnerability in Block Builder Logic

BlockBeats News, June 27th

On June 27th, the Base engineering team released a retrospective of the block production interruption event that occurred on June 25th. The Base mainnet experienced two block production interruptions on June 25th and June 26th. The first event occurred on June 25th at 11:47 ET and lasted for 116 minutes. The second event occurred on June 26th at 11:28 and lasted for 20 minutes. The root cause of both events was the same. The chain's integrity was not compromised, and all funds on Base remained secure. Block production safely resumed after the team mitigated the events.

The fundamental issue was a vulnerability in the sorter's block construction logic, which led to an outdated log state not being cleared after a transaction failed validation. An invalid transaction was accepted by the block builder and executed as expected to fail. However, the system incorrectly retained the log state containing accessed accounts and storage slots. Subsequently, a valid transaction was executed before the log state was properly cleared, resulting in mismatched Gas fees and the creation of a block with an invalid state transition. Other nodes could not accept this block, causing the chain to halt entirely.

During the event, Base was unable to produce new L2 blocks, and the sorter and validator nodes could not move past the invalid block to progress. New transactions could not be added to the chain. The team patched the sorter to ensure the correct updating of the log state during execution to fix the interruption. Base stated that they would enhance protocol fuzz testing and load testing tools to more easily identify adversarial transaction patterns that could expose similar vulnerabilities. They will also continue to improve operational and monitoring capabilities.