Ankr bridge drained after attacker reused an already-redeemed deposit

Someone walked off with tokens from Ankr's Ethereum cross-chain bridge on Nov. 9, and the contract never hit the brakes. Five withdrawals landed in the same wallet between 3:09:35 a.m. and 3:11:59 a.m. ET, moving ankrETH, ankrPOL, ANKR, aMATICb and aETHb. Three of those assets carried price tags worth roughly $303,600 based on Etherscan's displayed values at 3:46 a.m. ET — a figure that leaves out the two unpriced tokens and says nothing about what the attacker actually sold them for.

By 3:49 a.m. ET, the bridge's transaction list showed nothing new, a zero ETH balance and $0 in priced Ethereum token holdings. Its public pause flag still read false, so containment wasn't confirmed. Blockaid had flagged an 'ongoing exploit' seven minutes earlier, at 3:42 a.m. ET, saying the attacker used a small Optimism deposit to unlock the bridge's inventory.

That deposit is the whole trick. All five withdrawals pointed back to the same Nov. 3 Optimism transaction, which put up just 0.0044024803 ankrETH — and that amount had already been withdrawn on Ethereum on Nov. 3. The fresh withdrawal calls carried altered receipt data naming a different recipient, bigger amounts and different output tokens.

Ankr's own documentation lays out how the bridge is meant to work: users deposit on one network, the transaction goes to Ankr's backend for notarization, and they withdraw on the destination chain. The deployed implementation demands authorization from a designated signer before any funds move. Records show the withdrawals cleared that gate — they don't show how the attacker got authorization the system accepted.