Although initially inconspicuous in its manifestation, the Cardano network experienced a substantive chain split on November 21, 2025, when a malformed delegation transaction, exploiting a latent bug in a core library dating to 2022, precipitated a bifurcation into a “poisoned” and a “healthy” ledger, a divergence driven by heterogeneous node behavior whereby newer node versions accepted the malformed payload while legacy implementations rejected it, producing validation asymmetry that orphaned blocks, fragmented block production, and materially impaired consensus finality across stake pools and decentralized finance protocols. The malformed delegation was constructed using an AI-generated script that obfuscated intent and exploited a long-standing validation gap, a vector that prompted immediate AI forensics analysis to trace the genesis of the payload to a wallet associated with a former testnet participant, while public statements characterized the act as a deliberate intrusion, prompting regulatory notification and an FBI investigation. Technical telemetry revealed that block producers and validators diverged along software-version lines, resulting in asynchronous chain heads, slowed block production, and measurable reward losses for validators whose signatures accumulated on the orphaned, “poisoned” branch, conditions that temporarily enabled double-spending scenarios and disrupted liquidity provisioning within automated market makers and lending protocols. Such chain splits are often resolved through longest chain rules, which helped guide the emergency response. The emergency response prioritized issuance of a corrective patch to remediate the underlying library defect, distribution of network-wide upgrade instructions, and direct engagement with stake pool operators to expedite adoption, actions which, coordinated with enhanced monitoring, facilitated reintegration of the bifurcated ledger and restoration of systemic consensus following rapid version harmonization. Institutional and community governance mechanisms were scrutinized in the aftermath, intersect, Cardano’s governance body, publishing a post-mortem that catalyzed debate over whether the incident constituted an orchestrated attack or a misapplied experiment, while governance reforms were proposed to strengthen pre-deployment review, mandate extended stress testing, and formalize incident escalation protocols, measures intended to reduce latent-risk accrual. The episode underscored emergent systemic risks from automated code generation, highlighted deficiencies in protocol-level comprehension among some developers, and stimulated commitments to expanded audits, enhanced AI forensics capabilities, and rigorous governance oversight to protect network integrity and restore market confidence. Developers from IOG and the Cardano Foundation quickly deployed a hotfix that merged the divergent chains and restored normal operations within hours, an intervention that resolved the issue. Recent reports confirmed that user funds remained secure, with no customer assets lost during the incident user funds unaffected.
