Multichain's token contracts for WETH, PERI, OMT, WBNB, MATIC, and AVAX lacked proper validation of ERC20 permit() function calls. An attacker exploited this vulnerability to steal tokens from users who had previously granted approvals. A white-hat responder later returned approximately $1M of the $3M total loss, retaining 62 ETH as a bounty.

The cross-chain bridge Multichain said that an important vulnerability affecting six tokens of WETH, PERI, OMT, WBNB, MATIC, and AVAX was officially discovered. Now the vulnerability has been successfully repaired, and all users' assets are safe and cross-chain. Transactions will not be affected. However, if the user has authorized these six assets, he needs to log in as soon as possible to revoke the authorization, otherwise the assets may be at risk. According to the official announcement on the 19th, because some users did not cancel the authorization in time, the stolen funds were about 445 WETH, worth about 1.43 million US dollars.