_curveSwap() wrong formula

[code423n4]

Lines of code

https://github.com/code-423n4/2023-08-dopex/blob/eb4d4a201b3a75dd4bddc74a34e9c42c71d0d12f/contracts/core/RdpxV2Core.sol#L546

Vulnerability details

Impact

RdpxV2Core._curveSwap An error in the formula for calculating the minimum amount of minOut for dpxEth may cause the slippage protection to fail.

Proof of Concept

_curveSwap()The code implementation is as follows:

  function _curveSwap(
    uint256 _amount,
    bool _ethToDpxEth,
    bool validate,
    uint256 minAmount
  ) internal returns (uint256 amountOut) {
    IStableSwap dpxEthCurvePool = IStableSwap(addresses.dpxEthCurvePool);

    // First compute a reverse swapping of dpxETH to ETH to compute the amount of ETH required
    address coin0 = dpxEthCurvePool.coins(0);
    (uint256 a, uint256 b) = coin0 == weth ? (0, 1) : (1, 0);

    // validate the swap for peg functions
    if (validate) {
      uint256 ethBalance = IStableSwap(addresses.dpxEthCurvePool).balances(a);
      uint256 dpxEthBalance = IStableSwap(addresses.dpxEthCurvePool).balances(
        b
      );
      _ethToDpxEth
        ? _validate(
          ethBalance + _amount <= (ethBalance + dpxEthBalance) / 2,
          14
        )
        : _validate(
          dpxEthBalance + _amount <= (ethBalance + dpxEthBalance) / 2,
          14
        );
    }

    // calculate minimum amount out
    uint256 minOut = _ethToDpxEth
@>    ? (((_amount * getDpxEthPrice()) / 1e8) -
        (((_amount * getDpxEthPrice()) * slippageTolerance) / 1e16))
      : (((_amount * getEthPrice()) / 1e8) -
        (((_amount * getEthPrice()) * slippageTolerance) / 1e16));

    // Swap the tokens
    amountOut = dpxEthCurvePool.exchange(
      _ethToDpxEth ? int128(int256(a)) : int128(int256(b)),
      _ethToDpxEth ? int128(int256(b)) : int128(int256(a)),
      _amount,
      minAmount > 0 ? minAmount : minOut
    );
  }

From the code above we know that if _ethToDpxEth=true uses the formula
minOut = (((_amount * getDpxEthPrice()) / 1e8) - (((_amount * getDpxEthPrice()) * slippageTolerance) / 1e16))

but getDpxEthPrice() is the dpxEth price.

The correct formula should be _amount * 1e8 / getDpxEthPrice()

Tools Used

Recommended Mitigation Steps

  function _curveSwap(
    uint256 _amount,
    bool _ethToDpxEth,
    bool validate,
    uint256 minAmount
  ) internal returns (uint256 amountOut) {
....

    // calculate minimum amount out
-   uint256 minOut = _ethToDpxEth
-    ? (((_amount * getDpxEthPrice()) / 1e8) -
-       (((_amount * getDpxEthPrice()) * slippageTolerance) / 1e16))
-     : (((_amount * getEthPrice()) / 1e8) -
-       (((_amount * getEthPrice()) * slippageTolerance) / 1e16));


+   uint256 minOut = _ethToDpxEth
+    ? (((_amount * 1e8) / getDpxEthPrice()) * （1e8 - slippageTolerance） / 1e8
+     : (((_amount * 1e8) / getEthPrice()) * （1e8 - slippageTolerance） / 1e8;

    // Swap the tokens
    amountOut = dpxEthCurvePool.exchange(
      _ethToDpxEth ? int128(int256(a)) : int128(int256(b)),
      _ethToDpxEth ? int128(int256(b)) : int128(int256(a)),
      _amount,
      minAmount > 0 ? minAmount : minOut
    );
  }

Assessed type

Context

[c4-pre-sort]

bytes032 marked the issue as duplicate of #2172

[c4-pre-sort]

bytes032 marked the issue as sufficient quality report

[c4-pre-sort]

bytes032 marked the issue as duplicate of #970

[c4-judge]

GalloDaSballo marked the issue as satisfactory