Numbers Protocol's bridge integration with Multichain exposed a vulnerability in how excessive permissions were handled in the permit mechanism. An attacker exploited a user's unlimited permit grant to steal 557,754 NUM tokens, converting them to 13 ETH and draining multiple user accounts.

According to the intelligence of the SlowMist security team, the Numbers Protocol (NUM) token project on the ETH chain was attacked, and the attacker made a profit of about $13,836. The main reason for this attack is that the NUM token does not have a permit function and has a callback function, so a fake signature can be passed in to deceive the cross-chain bridge and cause the user's assets to be transferred out unexpectedly.