Chain partition

You may be aware that Cardano suffered a partition on the Mainnet at approximately 08:00UTC on November 21st 2025 which resulted in a reduction in blocks produced and slower transaction processing for around 12 hours while the issue was addressed.

The issue was caused by a crypto library dependency that allowed an invalid transaction to be introduced on some later node versions, but which was rejected by earlier versions. This caused a partition where later nodes considered the canonical chain version to include this malformed transaction, and diverge from the chain maintained by the earlier nodes.

The solution required the majority of Stake Pool Operators running the affected node versions to upgrade to a version which fixed the library dependency. ADAvault was running a version of the node that was affected and we upgraded all affected nodes to version 10.5.2 by 12:30UTC. All other operations were verified as operating correctly by 15:00UTC. Subsequently we have upgraded to 10.5.3 across all environments as this version supports an additional header type which will help diagnostics.

Midnight testnet-02 was also affected due to their dependency on the Cardano Preview testnet, and has now resumed operations.

Somewhat ironically the need for all parties around the world to come together quickly to address this issue has proved the resilience and strength of the ecosystem and will likely result in a positive long term outcome, even if the short time impact would have been good to avoid.

Lots of updates on X on the topic including this one from Charles…