A Single Flawed Transaction Splits Cardano Into Two Chains

On November 21, 2025, Cardano suffered its most serious technical failure in nearly a decade, when a single flawed delegation transaction triggered a rare chain split—effectively causing the blockchain to divide into two competing versions of itself.

The malformed transaction exploited a years-old bug buried deep within Cardano’s core software library, a vulnerability that had remained dormant until a developer accidentally activated it.

When the code was executed, Cardano’s mainnet diverged into a “poisoned” chain containing the faulty transaction and a “healthy” chain that rejected it, creating temporary delays, block production conflicts, and widespread uncertainty across the network.

Engineers immediately mobilized, coordinating an emergency fix and node upgrade that restored consensus and fully stabilized the chain within roughly 14.5 hours.

The Developer Behind the Incident Faces Legal Scrutiny

Soon after the incident, a developer came out to confess to being the culprit behind the incident, saying that it was an unintended result of following AI-generated instructions without proper validation on a testnet.

He added that he only understood the full scale of the mistake only when the block production appeared frozen on public explorers.

He clarified that the transaction was never meant to be malicious and that he stressed that he didn't sell or short ADA before or during the disruption—an explicit clarification to show that he didn't potentially profit from the event.

Despite the apology, Cardano founder Charles Hoskinson has reported the incident to the local authorities. Hoskinson voiced his skepticism towards Homer's apology, claiming he was only trying to walk it back now that the FBI is involved.

Hoskinson described the act as careless but targeted, underscoring the broader implications of a single developer being able to trigger a protocol-level failure.

Resignations and Rising Legal Concerns Inside the Ecosystem

The chain split also prompted major exchanges such as Coinbase to temporarily halt ADA deposits and withdrawals to ensure ledger accuracy while waiting for final chain confirmation.

Although no user funds were lost, the disruption brought renewed attention to the legal and personal risks associated with critical blockchain infrastructure work.

Following internal review, an employee at Input Output Global publicly resigned, citing concerns about the potential legal exposure developers face when errors inside mission-critical codebases lead to network-wide consequences.

The departure added further weight to the ongoing investigation, reflecting the seriousness with which both the company and the broader community are treating the incident.

Despite the turmoil, Cardano leadership emphasized unity and long-term resilience, calling the event a stark reminder of the importance of rigorous testing, responsible development practices, and continuous audits for vulnerabilities—even those that have existed, unseen, for years.

As the network moves forward, the incident stands as both a cautionary tale and a catalyst for strengthening Cardano’s infrastructure, ensuring that no single flawed transaction can jeopardize the integrity of the chain again.