Key Highlights
- Developer Homer J took responsibility, saying he followed AI instructions without proper testing, causing network disruption.
- Charles Hoskinson called it a deliberate attack on his pool; the FBI is investigating it as a major cyber incident.
- Cardano quickly restored the network with patched nodes, data reconciliation, and a contingency plan to fix the split.
On November 21, 2025, the Cardano blockchain experienced a rare and dramatic split into two chains, exposing a hidden bug and raising questions about how strong the network really is.
It started with one malformed delegation transaction that a pseudonymous developer called Homer J executed. The transaction caused unexpected behavior in newer node software, creating what experts termed a “poisoned” chain. The identical transaction was refused by older nodes, which then formed a parallel “healthy” chain.
According to a post-mortem report by Cardano ecosystem governance body, Intersect, the split occurred because the transaction exploited a bug in the deserialization code. Intersect noted that the bug had existed since 2022 but only showed up in recent node versions when used with specialized tools.
How the incident unfolded
The chain split began around 08:00 UTC on November 21, following a similar problem seen on the Preview testnet the day before. The malformed transaction went through on newer nodes but was rejected by older ones, creating a disagreement that split the network.
On November 22, Homer J. took responsibility for posts on X. He explained that the incident began as a personal challenge to reproduce a known bad transaction.
He admitted he had carelessly followed AI-generated instructions to block traffic on his Linux server without testing it on the testnet first. “I watched in horror as block explorers froze and the network became disrupted,” he wrote.
Homer J. stressed that he had no malicious intent, did not profit financially, and did not manipulate ADA’s price. “I’m ashamed of my carelessness and take full responsibility for it,” he said, expressing deep remorse and calling himself “a bad human being” for the stress he caused the community.
Charles Hoskinson’s comments and the FBI investigation
In a tweet shortly after the incident, Cardano co-founder Charles Hoskinson characterized the chain split as a premeditated attack by a disgruntled SPO who had been trying for months to harm the brand and reputation of Input Output Global (IOG).
Hoskinson explained that the attacker had targeted his personal staking pool and, as a result, brought down the entire network.
He said that, because of this, SPOs were suffering from lost block rewards, there was a high probability of double-spends, and DeFi protocols were affected. He warned that fully restoring the network and repairing reputational damage could take weeks.
Hoskinson further confirmed that the incident was under investigation by the U.S. Federal Bureau of Investigation as a major cyberattack. He said it affected “the lives, money, and commerce of millions of people,” comparing it to an attempt to disrupt a national economy.
Cardano’s response
As noted in the Intersect report, The Cardano ecosystem swiftly to restore stability:
- Node upgrades: Fixed node versions 10.5.2 and 10.5.3 were released to fix the deserialization bug. Stake Pool Operators (SPOs), exchanges, and relay operators were asked to upgrade their nodes immediately. Following the Ouroboros consensus rules, the healthy chain gradually became dominant. The invalid blocks from the poisoned chain were removed.
- Data Reconciliation: Intersect created a team that worked to align transactions from both chains and ensured smooth convergence.
- Investigation and Legal Action: The wallet responsible was traced to a former Incentivized Testnet participant, and authorities, including the FBI, are investigating.
- Contingency Planning: A disaster recovery plan based on CIP 135 was prepared in order to guide the network towards the correct chain if upgrades were delayed.
Community reaction
The Cardano community responded with concern, criticism, and some sympathy. While some of the community members blamed Homer J, many supported him, emphasizing the network’s resilience and emphasized that the incident exposed vulnerabilities in Cardano’s code.
However, given the nature of the exploit, no user funds were lost. Most wallets, including Daedalus, safely ignored the malformed transaction and were unaffected. Block production kept going on both chains, but some apps and block explorers showed mixed or inconsistent data. For safety measures, major exchanges like Coinbase temporarily paused ADA deposits and withdrawals.
Following the incident, ADA’s price fell by more than 6% but recovered in the following trading sessions. According to CoinMarketCap, ADA has dropped around 18% over the past week, with trading currently around $0.4073.
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