THORChain halted trading on ten blockchains after an Ethereum one-block reorg on October 31 caused the protocol to pay out 10 ETH that a vault never received. The user has since returned the 10 ETH, and the vault is solvent again, but the affected chains remain paused until node operators decide it is safe to resume.
How the overpayment happened
THORChain said the reorg occurred at 11:34 UTC on October 31 and lasted only one block. A 10 ETH deposit to one vault sat in the dropped block and never landed on the canonical chain, but THORChain had already observed and credited it. The protocol therefore treated the funds as received, creating a mismatch between its ledger and the vault.
The swap tied to that deposit missed its price limit, so the protocol issued a refund. As a result, the vault paid out 10 ETH it never received. The sender’s real deposit was also refunded.
Every node detected the reorg, but the re-check intended to remove the deposit could not get a clear answer in time. The system then finalized the deposit, leaving the vault with a 10 ETH shortfall.
Emergency halts and current chain status
The automatic solvency checker detected the shortfall and halted ETH swaps. Within approximately two minutes, node operators paused ETH transaction signing, preventing further ETH from leaving the vaults. Three node votes then halted all ETH outbound payments, and three more votes halted all chains as a precaution while core developers investigated.
THORChain also outlined how emergency halts work. Three node votes can trigger a halt to protect network solvency, four counter votes can reverse it, and five votes can reverse that reversal. According to the team, halting a chain does not give those nodes control of the assets.
Trading remains active on AVAX, BASE, RUNE, and XRPL. The halted chains are ATOM, BCH, BSC, BTC, DOGE, ETH, LTC, SOL, TRON, and ZEC. Nodes will decide when to re-enable each chain once they deem it safe.
Remaining concern
A further concern remains now that the incident is public. During a reorg on an external chain, a malicious actor could submit a transaction with the same nonce, and the vaults would then pay that actor funds. Core developers have been working on the necessary fixes.
