## Description Within the functions `ThunderLoan::getCalculatedFee()` and `ThunderLoanUpgraded::getCalculatedFee()`, an issue arises with the calculated fee value when dealing with non-standard ERC20 tokens. Specifically, the calculated value for non-standard tokens appears significantly lower compared to that of standard ERC20 tokens. ## Vulnerability Details //ThunderLoan.sol ```solidity function getCalculatedFee(IERC20 token, uint256 amount) public view returns (uint256 fee) { //slither-disable-next-line divide-before-multiply @> uint256 valueOfBorrowedToken = (amount * getPriceInWeth(address(token))) / s_feePrecision; @> //slither-disable-next-line divide-before-multiply fee = (valueOfBorrowedToken * s_flashLoanFee) / s_feePrecision; } ``` ```solidity //ThunderLoanUpgraded.sol function getCalculatedFee(IERC20 token, uint256 amount) public view returns (uint256 fee) { //slither-disable-next-line divide-before-multiply @> uint256 valueOfBorrowedToken = (amount * getPriceInWeth(address(token))) / FEE_PRECISION; //slither-disable-next-line divide-before-multiply @> fee = (valueOfBorrowedToken * s_flashLoanFee) / FEE_PRECISION; } ``` ## Impact Let's say: - user_1 asks a flashloan for 1 ETH. - user_2 asks a flashloan for 2000 USDT. ```solidity function getCalculatedFee(IERC20 token, uint256 amount) public view returns (uint256 fee) { //1 ETH = 1e18 WEI //2000 USDT = 2 * 1e9 WEI uint256 valueOfBorrowedToken = (amount * getPriceInWeth(address(token))) / s_feePrecision; // valueOfBorrowedToken ETH = 1e18 * 1e18 / 1e18 WEI // valueOfBorrowedToken USDT= 2 * 1e9 * 1e18 / 1e18 WEI fee = (valueOfBorrowedToken * s_flashLoanFee) / s_feePrecision; //fee ETH = 1e18 * 3e15 / 1e18 = 3e15 WEI = 0,003 ETH //fee USDT: 2 * 1e9 * 3e15 / 1e18 = 6e6 WEI = 0,000000000006 ETH } ``` The fee for the user_2 are much lower then user_1 despite they asks a flashloan for the same value (hypotesis 1 ETH = 2000 USDT). ## Recommendations Adjust the precision accordinly with the allowed tokens considering that the non standard ERC20 haven't 18 decimals.