THORChain halts swaps after block reorg bug, slowing Binance hackers

THORChain node operators paused swaps involving assets on 10 networks, including Bitcoin, Ethereum, Solana and Tron.

THORChain halted swaps across multiple blockchains on Saturday after an Ethereum block reorganization exposed a refund bug, which may have inadvertently slowed the movement of funds stolen from Binance, according to Chainalysis.

According to THORChain, the incident began at 11:34 UTC on Saturday, when a one-block reorganization on Ethereum removed a 10 ETH deposit that THORChain had already credited. When the swap failed to meet its price limit, THORChain issued a refund against funds the vault had never received. The sender’s actual deposit was also refunded, resulting in an extra 10 ETH payout, which then triggered an automatic pause. 

An Ethereum block reorganization, or reorg, happens when the network replaces a recent block with a competing block. The newly discovered flaw lets THORChain refund a payment that Ethereum no longer recognizes as having happened. A malicious actor could potentially exploit that mismatch.

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