sam_gmk - Loss in precision in StableOracleDAI

[sherlock-admin]

sam_gmk

medium

Loss in precision in StableOracleDAI

Summary

Vulnerability Detail

getPriceUSD in StableOracleDAI is used to get the price of DAI from multiple sources and return the average.

 (, int256 price, , , ) = priceFeedDAIETH.latestRoundData();

    	return
        	(wethPriceUSD * 1e18) /
        	((DAIWethPrice + uint256(price) * 1e10) / 2);

Both DAIWethPrice and price return 1e18 decimals. Therefore there is no need to multiply the value by 1e10. Since price is an ETH pair, the returned decimals are 1e18 and not 1e8.

POC:

address public priceFeedDAIETH = 0x773616E4d11A78F511299002da57A0a94577F1f4;

function testGetPriceUsd() external view returns (uint256) {
     uint8 numberOfDecimals = AggregatorV3Interface(priceFeedDAIETH).decimals();
      console.log("NUMBER OF DECIMALS:", numberOfDecimals);


     (, int256 price, , , ) = AggregatorV3Interface(priceFeedDAIETH).latestRoundData();
       uint256 finalPrice = uint256(price) * 1e10;
     console.log("REAL PRICE:", uint256(price));
     console.log("SUPER LARGE NUMBER:", finalPrice);


   }

Logs:
NUMBER OF DECIMALS: 18
REAL PRICE: 549993804800023
SUPER LARGE NUMBER: 5499938048000230000000000

Impact

Loss in precision when performing calculations

Code Snippet

https://github.com/sherlock-audit/2023-05-USSD/blob/main/ussd-contracts/contracts/oracles/StableOracleDAI.sol#L52

Tool used

Manual Review

Recommendation

Remove the 1e10 multiplication

Duplicate of #236