Yearn Finance details $9 million yETH exploit, confirms partial asset recovery and discloses repair plan

Following rumors, Yearn Finance has released a detailed post-mortem report on the yETH exploit last week, revealing a three-stage numerical error in its legacy stableswap liquidity pool that allowed attackers to 'mint' LP tokens indefinitely and steal approximately $9 million in assets from the pool.

Yearn has confirmed that with the assistance of the Plume and Dinero teams, they have successfully recovered 857.49 pxETH, representing about a quarter of the stolen assets. The team plans to distribute the recovered funds proportionally to yETH depositors.

The decentralized finance protocol stated that the exploit occurred on block 23,914,086 on November 30, 2025, where attackers manipulated the internal resolver of the liquidity pool into a divergent state through a complex sequence of operations, ultimately triggering arithmetic underflow. The attack targeted a custom stableswap pool aggregating various Liquidity Staking Tokens (LSTs) and a yETH/WETH Curve pool. Yearn emphasized that its v2 and v3 vaults and other products were not affected.

To address these issues, Yearn has disclosed a repair plan, including implementing explicit domain checks on the resolver, replacing insecure arithmetic with checked arithmetic in critical sections, and disabling bootstrapping logic after the pool goes live.

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