# SDAIPriceFeed is vulnerable to donation attack via manipulatable vault rate Crit/High · Sherlock · EUR stablecoin · 26th December 2025 Finding H-1 of the Evro Collateral Onboarding security review. - Report: /reports/evro-collateral-onboarding - Source: https://github.com/0xsimao/audits/blob/main/Sherlock/private-audits/2025-12-26-evro-finance-ii.pdf --- ## Summary The `SDAIPriceFeed` uses the instantaneous vault rate from `convertToAssets()` which can be manipulated through donation attacks, allowing attackers to drain the protocol. ## Vulnerability Detail The `SDAIPriceFeed` calculates the sDAI price using the ERC4626 vault's `convertToAssets()` function, which returns the current exchange rate between sDAI shares and DAI assets. This rate can be manipulated by donating assets directly to the vault. Attack scenario: 1. Attacker deposits 500 sDAI when vault has 500 sDAI shares and 500 DAI (1:1 rate) 2. Attacker donates 9000 DAI directly to the vault 3. Now 1000 sDAI shares = 10000 DAI (1:10 rate) 4. Attacker opens a trove with 1000 sDAI and borrows 10000 EVRO at the inflated rate 5. Attacker redeems the 10000 EVRO against other collaterals, draining the protocol ## Impact An attacker can manipulate the sDAI price to borrow significantly more EVRO than the collateral is worth, then redeem against other collaterals to drain the protocol. ## Code Snippet https://github.com/sherlock-audit/2025-12-evro-finance-dec-26th/blob/main/evro/contracts/src/PriceFeeds/SDAIPriceFeed.sol#L47 ```solidity function _fetchPricePrimary() internal returns (uint256, bool) { assert(priceSource == PriceSource.primary); (uint256 daiUSDPrice, bool daiEurOracleDown) = _getOracleAnswer(ethUsdOracle); (uint256 eurUsdPrice, bool eurUsdOracleDown) = _getOracleAnswer(eurUsdOracle); // Get the DAI rate of the SDAI vault uint256 sdaiDaiRate = sdai.convertToAssets(1e18); // @audit - manipulatable! // ... uint256 sdaiUSDPrice = FixedPointMathLib.mulWadUp(daiUSDPrice, sdaiDaiRate); lastGoodPrice = FixedPointMathLib.divWad(sdaiUSDPrice, eurUsdPrice); return (lastGoodPrice, false); } ``` ## Tool Used Manual Review ## Recommendation Use the max price between an oracle rate and the instantaneous rate for redemptions, and the min price for calculating ICR when opening/adjusting troves: ```solidity function _fetchPricePrimary(bool _isRedemption) internal returns (uint256, bool) { uint256 sdaiDaiRate = sdai.convertToAssets(1e18); (uint256 oracleRate, bool oracleDown) = _getOracleAnswer(sdaiOracle); uint256 rateToUse; if (_isRedemption) { rateToUse = LiquityMath._max(sdaiDaiRate, oracleRate); } else { rateToUse = LiquityMath._min(sdaiDaiRate, oracleRate); } // ... rest of calculation } ``` Disclosed by 0xSimao (https://0xsimao.com/). --- Related findings: - [Donation attack possible, although unlikely, could make an initial deposit](https://0xsimao.com/findings/aegis-donation-although-unlikely-deposit): Aegis Staked YUSD - [OffchainExchange::swapAmm() does not validate that txn.priceX18 > 0, allowing donation attacks](https://0xsimao.com/findings/vertex-offchain-validate-price-donation): Vertex - [Borrowing is not vulnerable to an inflation attack, it's unnecessary to borrow when initializing the vault](https://0xsimao.com/findings/fuji-finance-inflation-attack-borrow-initializing): Fuji Finance - [Missing priceFeedDisabled event in RedStonePriceFeedBase](https://0xsimao.com/findings/felix-price-disabled-red-stone): Felix Price Feeds