Grim Finance's GrimBoostVault lacked reentrancy guards. Attackers exploited this via nested calls during safeTransferFrom to accumulate false collateral through repeated deposits.

According to official sources, GrimFinance, a compound income platform on the Fantom chain, suffered a lightning loan attack, and the current loss has exceeded 30 million U.S. dollars. The attacker uses the function named "beforeDeposit()" in GrimFinance's vault strategy to attack and enter the malicious Token contract.