Caviar Private Pools - climber2002's results

Lines of code

https://github.com/code-423n4/2023-04-caviar/blob/cd8a92667bcb6657f70657183769c244d04c015c/src/PrivatePool.sol#L750-L752

Vulnerability details

Impact

The flashFee() doesn't consider exponent. So actual flashFee needed is much lower than expected.

Proof of Concept

In changeFee definition it has comments,

// The change/flash fee to 4 decimals of precision. For example, 0.0025 ETH = 25. 500 USDC = 5_000_000.
uint56 public changeFee;

And also in changeFeeQuote, it considered exponent

uint256 exponent = baseToken == address(0) ? 18 - 4 : ERC20(baseToken).decimals() - 4;
uint256 feePerNft = changeFee * 10 ** exponent;

However in flashLoan it uses changeFee directly,

// calculate the fee
uint256 fee = flashFee(token, tokenId);

// if base token is ETH then check that caller sent enough for the fee
if (baseToken == address(0) && msg.value < fee) revert InvalidEthAmount();

Let's suppose baseToken is address(0) and changeFee is 25, the expectation is the flashFee should be 0.0025ETH, however actually it only needs 25Wei to perform flash loan. That's much smaller than expected.

Tools Used

Manual Review

Recommended Mitigation Steps

In flashFee add exponent calculation

 function flashFee(address, uint256) public view returns (uint256) {
        uint256 exponent = baseToken == address(0)
            ? 18 - 4
            : ERC20(baseToken).decimals() - 4;
        return changeFee * 10 ** exponent;
 }