SlowMist: The root cause of the yearn attack is that the Yearn YETH pool contract contains unsafe mathematical operations.

Mars Finance News: According to monitoring by SlowMist, the decentralized finance protocol Yearn suffered a hacker attack, resulting in a loss of approximately $9 million. The SlowMist security team analyzed the incident and confirmed the root cause as follows: the vulnerability originated from the logic of the _calc_supply function used to calculate supply in the Yearn yETH Weighted Stableswap Pool contract. Due to unsafe mathematical operations, this function allowed overflows and rounding errors during calculations, leading to significant discrepancies in the product calculation of new supply and virtual balance. Attackers exploited this flaw to manipulate liquidity to specific values and excessively mint liquidity pool (LP) tokens, thereby gaining illegal profits. It is recommended to strengthen boundary scenario testing and adopt security-verified arithmetic mechanisms to prevent high-risk vulnerabilities such as overflow in similar protocols. Previously, Yearn issued a statement saying that its yETH stable pool was attacked at 21:11 UTC on November 30, with the attacker minting large amounts of yETH through a custom contract, resulting in about $8 million of assets lost in the pool and an additional $900,000 lost from the yETH-WETH pool on Curve.