• Malformed transaction caused validation mismatch between node versions, splitting the chain temporarily.

• Stake pool operators confirmed block production never halted despite the incident.

• ADA price dropped 5.9% to $0.4013 in the 24 hours following the event, per market data.

Discover how Cardano’s chain split unfolded due to a software flaw and the swift response that restored network integrity. Stay informed on blockchain security—explore Cardano updates today.

What Caused the Cardano Chain Split in 2025?

Cardano chain split occurred when a malformed delegation transaction passed validation on newer node versions but was rejected by older ones, creating two diverging chains. According to Intersect, Cardano’s governance organization, this exploited a bug in an underlying software library not caught by validation code. Developers responded rapidly with a hard fork, merging the chains and maintaining network functionality without downtime.

How Was the Malformed Transaction Responsible for Cardano’s Network Divergence?

The incident began around 8 AM UTC on Friday, November 21, 2025, when the faulty transaction entered the ledger on one branch while older nodes refused it, as detailed in Intersect’s incident report. This led to the “bad chain” accumulating more stake weight initially, growing faster than the valid one, according to staking pool operator Markus from Cliopool. Charles Hoskinson, Cardano co-founder, described it as a premeditated attack by a disgruntled stake pool operator, identifying the wallet linked to an Incentivized Testnet participant. Relevant authorities, including the Federal Bureau of Investigation, were notified for investigation. Expert analysis from blockchain security firms highlights that such bugs underscore the need for robust software audits, with Intersect confirming no user funds were lost but some stake pool operators faced temporary reward disruptions due to double spends. The resolution involved urging all stake pool operators to update to version 10.5.3, ensuring convergence.

Frequently Asked Questions

What Impact Did the Cardano Chain Split Have on Users and Stake Pool Operators?

The Cardano chain split affected every user by creating temporary ledger divergence, leading to potential double spends that caused stake pool operators to lose block rewards temporarily. Intersect reported no permanent fund losses, and block production continued seamlessly. Cleanup efforts are expected to take weeks, per Hoskinson’s assessment, but the network’s resilience prevented broader downtime.

Was the Cardano Chain Split Incident a Deliberate Attack?

According to Charles Hoskinson, the Cardano chain split stemmed from a deliberate act by a disgruntled stake pool operator aiming to damage the network’s reputation. An X user named Homer J. later claimed responsibility, admitting it started as a personal challenge to test bad transactions using AI-generated instructions. They apologized, stating no malicious intent, though authorities are investigating.

Key Takeaways

• Network Resilience Demonstrated: Despite the split, Cardano’s protocol kept running without halting block production, showcasing robust design.
• Rapid Response Key: Developers forked, fixed the issue, and identified the source within one day, with updates distributed to merge chains swiftly.
• Ongoing Investigation: Authorities like the FBI are involved, emphasizing the seriousness of exploiting software flaws in blockchain ecosystems.

Conclusion

The Cardano chain split incident of 2025, triggered by a malformed transaction exploiting a validation bug, highlighted vulnerabilities in node software while affirming the blockchain’s quick recovery mechanisms. With Intersect’s detailed reporting and Hoskinson’s insights, the event reinforces the importance of continuous updates and security vigilance in decentralized networks. As Cardano evolves, stakeholders should prioritize software patches to mitigate future risks and sustain trust in its ecosystem.