Immunefi Audit Competitions
Alchemix V3

56346 sc insight redundant calculation of feeamount in repay function

Submitted on Oct 14th 2025 at 19:04:52 UTC by @magtentic for Audit Comp | Alchemix V3

Description

Brief/Intro

In the repay function of the contract, the protocol fee is calculated and stored in the feeAmount variable.
However, the same calculation is repeated multiple times later in the function instead of reusing the variable.

Vulnerability Details

Within the repay function, there are multiple places where the same calculation is been done creating redundant code where as the calculation has already been done in feeAmount, the values used for the calculation do not change so it is safe to use the variable feeAmount.

    function repay(uint256 amount, uint256 recipientTokenId) public returns (uint256) {
        ...
        // Debt is subject to protocol fee similar to redemptions
        uint256 feeAmount = creditToYield * protocolFee / BPS;
        ...
        } else {
            account.collateralBalance -= creditToYield * protocolFee / BPS;
        }
        ...
        TokenUtils.safeTransfer(myt, protocolFeeReceiver, creditToYield * protocolFee / BPS);
        _mytSharesDeposited -= creditToYield * protocolFee / BPS;
        ...
    }

creditToYield * protocolFee / BPS can be replaced by feeAmount

Impact Details

This is primarily a code optimization issue.
Reusing feeAmount improves:

  • Gas efficiency
  • Readability and maintainability
  • Reduces the risk of inconsistencies if the formula changes

References

Alchemist V3 contract - https://github.com/alchemix-finance/v3-poc/blob/immunefi\\_audit/src/AlchemistV3.sol

Proof of Concept

Insight showing code optimization within the repay function.