Caviar Private Pools - ToonVH's results

Lines of code

https://github.com/code-423n4/2023-04-caviar/blob/main/src/PrivatePool.sol#L416

Vulnerability details

Impact

The fee for a flashloan does not take the decimals of the underlying asset into account, and is statically calculated (=changeFee, regardless of flashloan size).

Proof of Concept

If a changeFee of 25 is set (= 0.0025 ETH as mentioned on line 87). The flashloan fee will only be 25 wei, not the intended 0.0025 ETH.

This is because flashfee simply returns the changeFee. It does not convert the changeFee from 4 decimals to the decimals of the basetoken.

function flashFee(address, uint256) public view returns (uint256) {
  return changeFee;
}

Additionally the flashfee is static and does not change depending on the value of the loaned NFT. However, it is unclear if this is intended behaviour.

Tools Used

Recommended Mitigation Steps

• Convert changeFee from 4 decimals to the basetokens decimals when calculating the flashfee
• (Calculate flashfee depending on the value of the loaned NFT)

Judge has assessed an item in Issue #225 as 2 risk. The relevant finding follows:

uint256 exponent = baseToken == address(0) ? 18 - 4 : ERC20(baseToken).decimals() - 4; will revert since ERC20(baseToken).decimals() - 4; causes an underflow