Uniswap V1

An attacker exploited a reentrancy vulnerability in Uniswap V1's imBTC liquidity pool using ERC777's callback mechanism. By calling deposit, triggering the ERC777 callback before balance updates, and immediately withdrawing, the attacker could drain tokens from the pool at artificial prices.

The Consensys team had discovered the vulnerability in 2019 but no exploitable ERC777 token existed until imBTC launched.