On Gnosis Chain, attackers exploited xDAI's non-standard _callAfterTransfer() callback reentrancy; using flashloans to stack borrows before balance updates, they withdrew amounts far exceeding collateral value.

The Agave contract on Gnosis Chain was attacked due to an untrusted external call. The attacker calls the liquidateCall function to liquidate himself without any debt. During the liquidation process, the liquidation contract called the attacker contract. During the process, the attack contract deposited 2728 WETH obtained through the flash loan and minted 2728 aWETH. And use this as collateral to lend out all available assets in the Agave project. After the external call ends, the liquidateCall function directly liquidates the 2728 aWETH previously deposited by the attacker and transfers it to the liquidator.