Bahurum - Incorrect decimals for price in StableOracleDAI.getPriceUSD()

[sherlock-admin]

Bahurum

high

Incorrect decimals for price in StableOracleDAI.getPriceUSD()

Summary

In StableOracleDAI, price is treated in computations as if it was 8 decimals, while it is in 18 decimals.

Vulnerability Detail

StableOracleDAI.getPriceUSD() takes the average of the UniV3 WETH-DAI TWAP price and the DAI/ETH Chainlink oracle price:

            ((DAIWethPrice + uint256(price) * 1e10) / 2);

Since DAI/ETH feed is in 18 decimals, the multiplication by 1e10 is incorrect.

Impact

DAI price used is incorrect, causing amounts minted with DAI to be incorrect.

Code Snippet

https://github.com/USSDofficial/ussd-contracts/blob/f44c726371f3152634bcf0a3e630802e39dec49c/contracts/oracles/StableOracleDAI.sol#L52

Tool used

Manual Review

Recommendation

Remove multiplication of price by 1e10.

        ...
-           ((DAIWethPrice + uint256(price) * 1e10) / 2);
+           ((DAIWethPrice + uint256(price)) / 2);
        ...

Duplicate of #236