Agave hack — March 2022

On 15 March 2022 Agave, an Aave fork running on Gnosis Chain (formerly xDai), was drained in a reentrancy attack. The same attacker hit Hundred Finance, a Compound fork on the same chain, three minutes later.

The weakness lay in the tokens rather than in the lending code. Assets bridged onto Gnosis Chain are non-standard: the bridge's token contracts call back into the receiving address on every transfer, through a hook the analyses name callAfterTransfer. Agave's paths handed control to the attacker's contract before the protocol updated its record of the debt. Funded by a WETH flash loan from SushiSwap, the attacker re-entered repeatedly inside a single transaction, each call seeing the same unchanged collateral balance, and drew far more than the position could support. Accounts differ on the exact entry point: security researcher Mudit Gupta and Solidity developer Shegen, who said she personally lost about $225,000, described reentrancy on the borrow path, while a later Coinmonks write-up routes the callback through Agave's liquidate function.

Agave paused its contracts, saying it was investigating and would update once it understood the situation. Hundred Finance paused markets across all chains.

The figures need care. CoinDesk, The Block and Cointelegraph reported only a combined loss of about $11 million across the two protocols and gave no split. The Agave-only figure comes from rekt.news, which tracked 2,116 ETH worth about $5.5 million sent to Tornado Cash from the Agave drain against 2,363 ETH worth about $6.2 million from Hundred Finance, for a combined $11.7 million. Agave never published its own audited loss figure. Assets taken across both protocols included WETH, WBTC, LINK, USDC, GNO and WXDAI. No arrests have been reported.