# Partially removing liquidity may underflow if the price of the pool has changed significantly Medium · Three Sigma · NFT perpetuals · 2nd January, 2024 Finding 3S-NFTPerp-L04 of the Nftperp Exchange security review. - Report: /reports/nftperp-i - Source: https://cdn.sanity.io/files/qoqld077/production/c19530de75e234ad15694b4563edb1fc9d2a3fd8.pdf --- ### Description [removeLiquidity()](https://github.com/nftperp/NFTPerp-V2-Contracts/blob/1c16f2010a851ac23aec73822d55388901bbe5e7/src/AMM.sol#L654-L655) updates the position quote and base amount based on the removed quote and base amounts. However, if the proportions changed since the position was opened, it may underflow. ### Recommendation Reduce the quote and base amounts of the position pro-rata to the removed shares. ### Status Addressed in the AMMRouter --- Related findings: - [Call _updateMarkPrice() whenever markPrice is changed](https://0xsimao.com/findings/nftperp-ii-mark-price-whenever-changed): Nftperp Matching Engine - [Index underflow is not protected against, although it has no impact as the pool with index type(uint256).max should not be registered](https://0xsimao.com/findings/nftperp-ii-index-underflow-impact-registered): Nftperp Matching Engine - [Unconditional lastUpdated advance in RangePool.sync leads to loss of streamed BMX when pool liquidity == 0](https://0xsimao.com/findings/bmx-unconditional-range-streamed-bmx): BMX - [Add a 0 address check on the pool when adding liquidity for greater verbosity](https://0xsimao.com/findings/nftperp-ii-add-adding-greater-verbosity): Nftperp Matching Engine