The Standard

Summary

The calculation for the amountOutMinimum doesn't account for fees that is reduced from the amountIn. This can result in a constant revert due to slippage and the fact that the amountIn is insufficient.

Vulnerability Details

In the swap() function we can see that a swapFee is charged to the user whenever they are executing a swap. This can be seen from the code snippet below:

We can see that the amountIn value reflects that a swap fee reduction is factored in. But at the same time the calculation for the amountOutMinimum does not factor this in, we can see this from the the code below:

Here we see that the function call calculateMinimumAmountOut() does not factor in the reduction in amount to be swapped due to the fees.

Impact

This can result in the swap() transaction constantly reverting due to the failure in accounting for the swap amount. In times of high volatility this can result in a user being liquidated when they should've been able to swap their funds, but instead losing it all to liquidations.

Tools Used

Manual Review

Recommendations

To solve this issue, the following code change can be made to reflect the change in amount to be swapped due to the value of fees charged to the user.