Asymmetry contest - codetilda's results

Lines of code

https://github.com/code-423n4/2023-03-asymmetry/blob/44b5cd94ebedc187a08884a7f685e950e987261c/contracts/SafEth/SafEth.sol#L63-L101

Vulnerability details

Impact

Calling stake() payable function when state variables are derivativeCount = 0 and pauseStaking = false can cause division by zero exception or msg.sender will receive 0 amount of SafETH tokens for his ETH (posible diapason from 0.5 up to 200 ETH).

Proof of Concept

SafETH.sol L63-101

Let's say contract deployed, but derivativeCount = 0 (it's initial value) and staking not paused pauseStaking = false (it's initial value).

@audit comments provided in the code below

    @audit For example, we call function with msg.value in diapason from 0.5 up to 200 ETH, but derivativeCount = 0, pauseStaking = false
  
    function stake() external payable {
    require(pauseStaking == false, "staking is paused");
    require(msg.value >= minAmount, "amount too low");
    require(msg.value <= maxAmount, "amount too high"); 
    
    @audit We pass all requires

    uint256 underlyingValue = 0;

    // Getting underlying value in terms of ETH for each derivative

    @audit derivativeCount = 0 , so we skip for loop below and don't compute underlyingValue which in this case equal zero

    for (uint i = 0; i < derivativeCount; i++)
        underlyingValue +=
            (derivatives[i].ethPerDerivative(derivatives[i].balance()) *
                derivatives[i].balance()) /
            10 ** 18; 

    uint256 totalSupply = totalSupply();
    uint256 preDepositPrice; // Price of safETH in regards to ETH
    if (totalSupply == 0)
        preDepositPrice = 10 ** 18; // initializes with a price of 1
    else preDepositPrice = (10 ** 18 * underlyingValue) / totalSupply;
    @audit if totalSupply > 0 then preDepositPrice = 0 because of underlyingValue = 0, preDepositPrice = 0 can cause division by zero in line 98  

    uint256 totalStakeValueEth = 0; // total amount of derivatives worth of ETH in system

    @audit in case derivativeCount = 0 we skip for loop below and we don't calculate totalStakeValueEth = 0;

    for (uint i = 0; i < derivativeCount; i++) {
        uint256 weight = weights[i];
        IDerivative derivative = derivatives[i];
        if (weight == 0) continue;
        uint256 ethAmount = (msg.value * weight) / totalWeight;

        // This is slightly less than ethAmount because slippage
        uint256 depositAmount = derivative.deposit{value: ethAmount}();
        uint derivativeReceivedEthValue = (derivative.ethPerDerivative(
            depositAmount
        ) * depositAmount) / 10 ** 18;
        totalStakeValueEth += derivativeReceivedEthValue;
    }

    // mintAmount represents a percentage of the total assets in the system

    @audit Here will be exception if preDepositPrice = 0 or result minAmount = 0, because of totalStakeValueEth = 0
    uint256 mintAmount = (totalStakeValueEth * 10 ** 18) / preDepositPrice; @audit Line 98
    
    _mint(msg.sender, mintAmount);
    @audit If in the line 98 we don't have an exception we receives 0 safEth for 0.5 up to 200 ETH.

    emit Staked(msg.sender, msg.value, mintAmount);
}

Recommended Mitigation Steps

Use additional require statement: require(derivativeCount != 0, "no derivatives");