In a flash loan reentrancy attack on Sunday, Omni, a non-fungible token (NFT) money market platform, lost roughly 1,300 ETH ($1.43 million), according to PeckShield. It seems a reentrancy-related hack. @ParallelFi @OMNI_xyz The stolen funds were just mixed via @TornadoCash https://t.co/Nyunlkk3rr pic.twitter.com/XxxVyX80Fq — PeckShield Inc. (@peckshield) July 10, 2022 Users can stake their NFTs with Omni in exchange for ether (ETH) tokens, typically from well-known collections like Bored Ape Yacht Club. The hacker used the Omni protocol’s reentrancy weakness in the attack. Reentrancy is a known issue in Solidity-coded projects that enables a malicious actor to cause a smart contract to call an untrusted contract externally. This external call enters the protocol before the original function, allowing it to repeatedly entered to deplete the protocol’s liquidity. NFTs Deposited as Collateral Yajin Zhou, CEO of the blockchain security firm BlockSec, describes the attack process, which claimed that the attacker deposited NFTs from a group called Doodles. These NFTs served as security for a loan of wrapped ETH (WETH). The attacker then withdrew all, but one of the NFTs deposited as collateral, taking advantage of the reentrancy weakness. This operation started a malicious callback function that benefited the attacker. This feature allowed the hacker to purchase more doodles with the borrowed money before paying off the loan. Doodle...
