Lines of code

https://github.com/code-423n4/2022-05-rubicon/blob/8c312a63a91193c6a192a9aab44ff980fbfd7741/contracts/rubiconPools/BathToken.sol#L557-L585

Vulnerability details

Impact

First depositor of the pool can break minting of the Bath Token shares

Proof of Concept

An attacker -who is the first one to deposit- sends 1 wei and bypasses (totalSupply == 0) condition.
Later a very large amount of donation to the pool and inflates the shares proportionality ratio.
Subsequent depositors instead have to deposit an equivalent sum to avoid minting 0 shares. Otherwise, their deposits accrue to the attacker who holds the only share.

    function _deposit(uint256 assets, address receiver)
        internal
        returns (uint256 shares)
    {
        uint256 _pool = underlyingBalance();
        uint256 _before = underlyingToken.balanceOf(address(this));

        // **Assume caller is depositor**
        underlyingToken.transferFrom(msg.sender, address(this), assets);
        uint256 _after = underlyingToken.balanceOf(address(this));
        assets = _after.sub(_before); // Additional check for deflationary tokens

        (totalSupply == 0) ? shares = assets : shares = (
            assets.mul(totalSupply)
        ).div(_pool);

        // Send shares to designated target
        _mint(receiver, shares);
        emit LogDeposit(
            assets,
            underlyingToken,
            shares,
            msg.sender,
            underlyingBalance(),
            outstandingAmount,
            totalSupply
        );
        emit Deposit(msg.sender, msg.sender, assets, shares);
    }

https://github.com/code-423n4/2022-05-rubicon/blob/8c312a63a91193c6a192a9aab44ff980fbfd7741/contracts/rubiconPools/BathToken.sol#L557-L585

Tools Used

Manual Review

Recommended Mitigation Steps

Ensure the number of shares to be minted is non-zero Uniswap V2 solved this problem by sending the first 1000 LP tokens to the zero address. The same can be done in this case i.e. when totalSupply() == 0, send the first min liquidity LP tokens to the zero address to enable share dilution.

code-423n4 / 2022-05-rubicon-findings