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DeFiFoundryOracle
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Submission Details
Severity: low
Valid

Loss of precision in `twapPriceInEther` due to division before multiplication

hash

Vulnerability Details

When calculating twapPriceInEther, twapPrice is divided by 1e6 before multiplication with 1e18 is done.

function baseOracleCircuitBreaker(
uint256 protocolPrice,
uint80 roundId,
int256 chainlinkPrice,
uint256 timeStamp,
uint256 chainlinkPriceInEth
) private view returns (uint256 _protocolPrice) {
// more code
​
if (invalidFetchData || priceDeviation) {
uint256 twapPrice = IDiamond(payable(address(this))).estimateWETHInUSDC(
Constants.UNISWAP_WETH_BASE_AMT, 30 minutes
);
uint256 twapPriceInEther = (twapPrice / Constants.DECIMAL_USDC) * 1 ether;

https://github.com/Cyfrin/2023-09-ditto/blob/a93b4276420a092913f43169a353a6198d3c21b9/contracts/libraries/LibOracle.sol#L64-L85

According to the above calculation, the twapPrice obtained would be precise upto 6 decimal places. Performing division before multiplying with 1e18 will result in loss of this precision and.

Example Scenario

twapPrice = 1902501929
twapPriceInEther = 1902000000000000000000
​
// if multiplication is performed earlier,
twapPriceInEther = 1902501929000000000000

Impact

Price used can have -1 (in 18 decimals) difference from the original price.

Recommendations

Perform the multiplication before division.

diff --git a/contracts/libraries/LibOracle.sol b/contracts/libraries/LibOracle.sol
index 23d1d0a..6962ad7 100644
--- a/contracts/libraries/LibOracle.sol
+++ b/contracts/libraries/LibOracle.sol
@@ -82,7 +82,7 @@ library LibOracle {
uint256 twapPrice = IDiamond(payable(address(this))).estimateWETHInUSDC(
Constants.UNISWAP_WETH_BASE_AMT, 30 minutes
);
- uint256 twapPriceInEther = (twapPrice / Constants.DECIMAL_USDC) * 1 ether;
+ uint256 twapPriceInEther = (twapPrice * 1 ether) / Constants.DECIMAL_USDC;
uint256 twapPriceInv = twapPriceInEther.inv();
if (twapPriceInEther == 0) {
revert Errors.InvalidTwapPrice();
Updates

Lead Judging Commences

0xnevi Lead Judge
almost 2 years ago
0xnevi Lead Judge almost 2 years ago
Submission Judgement Published
Validated
Assigned finding tags:

finding-535

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