Cardano network recovers after malformed transaction triggers chain partition

Key Takeaways

• A malformed transaction exploited a deserialization bug, causing a temporary chain split on the Cardano mainnet.
• Engineers released hotfixes and node upgrades to resolve the issue, with no user funds compromised.

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The Cardano blockchain is returning to normal following a rare chain partition that temporarily split the network into two versions of its ledger.

According to a new report from Intersect, an organization supporting Cardano’s continuity and long-term development, the incident was triggered by a crafted, malformed delegation transaction on November 20.

The transaction exploited a cryptographic library bug dating back to 2022 on the Preview testnet, which allowed the network to split into two distinct chains, including “one containing the ‘poisoned’ transaction and a ‘healthy’ chain without it.”

Cardano engineers worked overnight to issue a hotfix after a malformed delegation transaction on the testnet exposed a bug. The next morning, the same type of transaction hit the mainnet, causing the network to split into two parallel chains.

Operators and other stakeholders quickly responded by upgrading nodes to version 10.5.3, effectively converging the network back to a single chain.

The team says no user funds were affected. The wallet behind the malformed transaction has been identified, with early forensics suggesting ties to a former Incentivized Testnet participant.

The FBI has been contacted to investigate the event as a possible cyberattack.

“Cardano is a family, and sometimes we fight and sometimes we have bad days and good days. And it’s not lost on me how difficult 2025 has been for us all,” said Cardano founder Charles Hoskinson in a statement. “The network survived. It didn’t stop.”

Following the Intersect report, an X user who goes by the name “Homer J” publicly admitted to triggering the malformed transaction that caused the incident.

He described it as a careless experiment that unintentionally caused the Cardano network to split and sent an apology, saying he felt awful about the disruption and had no malicious intent.

In response, Hoskinson said the troublemaker is now trying to walk it back after realizing the FBI is involved.

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