Yieldy contest - cccz's results

Lines of code

https://github.com/code-423n4/2022-06-yieldy/blob/524f3b83522125fb7d4677fa7a7e5ba5a2c0fe67/src/contracts/Staking.sol#L428-L447

Vulnerability details

Impact

In the stake function of the Staking contract, anyone can stake tokens for others. And each time a token is staked, the lock time of all tokens is increased. This allows an attacker to stake few tokens for others to increase the lock time of others' tokens.

        if (warmUpPeriod == 0) {
            IYieldy(YIELDY_TOKEN).mint(_recipient, _amount);
        } else {
            // create a claim and mint tokens so a user can claim them once warm up has passed
            warmUpInfo[_recipient] = Claim({
                amount: info.amount + _amount,
                credits: info.credits +
                    IYieldy(YIELDY_TOKEN).creditsForTokenBalance(_amount),
                expiry: epoch.number + warmUpPeriod
            });

            IYieldy(YIELDY_TOKEN).mint(address(this), _amount);
        }

Proof of Concept

https://github.com/code-423n4/2022-06-yieldy/blob/524f3b83522125fb7d4677fa7a7e5ba5a2c0fe67/src/contracts/Staking.sol#L428-L447

Tools Used

None

Recommended Mitigation Steps

Consider only allowing users to stake tokens for themselves

Lines of code

https://github.com/code-423n4/2022-06-yieldy/blob/524f3b83522125fb7d4677fa7a7e5ba5a2c0fe67/src/contracts/Staking.sol#L157-L160

Vulnerability details

Impact

The setCurvePool function of the Staking contract is used to update the CURVE_POOL variable, but the TOKE_POOL is not approved to the new CURVE_POOL in the setCurvePool function, which causes the instantUnstakeCurve function to not work.

Proof of Concept

https://github.com/code-423n4/2022-06-yieldy/blob/524f3b83522125fb7d4677fa7a7e5ba5a2c0fe67/src/contracts/Staking.sol#L157-L160

Tools Used

None

Recommended Mitigation Steps

    function setCurvePool(address _curvePool) external onlyOwner {
+      IERC20(TOKE_POOL).approve(CURVE_POOL, 0);       
        CURVE_POOL = _curvePool;
+      IERC20(TOKE_POOL).approve(CURVE_POOL, type(uint256).max);
        setToAndFromCurve();
    }

Lines of code

https://github.com/code-423n4/2022-06-yieldy/blob/524f3b83522125fb7d4677fa7a7e5ba5a2c0fe67/src/contracts/Staking.sol#L701-L719

Vulnerability details

Impact

In the staking contract, the rebase function can only be called once per epoch. In the rebase function, the rewards of the current epoch are used in the next epoch, which can cause the rewards to be updated incorrectly and lead to incorrect distribution of user rewards.

    function rebase() public {
        // we know about the issues surrounding block.timestamp, using it here will not cause any problems
        if (epoch.endTime <= block.timestamp) {
            IYieldy(YIELDY_TOKEN).rebase(epoch.distribute, epoch.number); // 懒更新

            epoch.endTime = epoch.endTime + epoch.duration;
            epoch.timestamp = block.timestamp;
            epoch.number++;

            uint256 balance = contractBalance();
            uint256 staked = IYieldy(YIELDY_TOKEN).totalSupply();

            if (balance <= staked) {
                epoch.distribute = 0;
            } else {
                epoch.distribute = balance - staked;
            }
        }
    }

Proof of Concept

https://github.com/code-423n4/2022-06-yieldy/blob/524f3b83522125fb7d4677fa7a7e5ba5a2c0fe67/src/contracts/Staking.sol#L701-L719

Tools Used

None

Recommended Mitigation Steps

Put IYieldy(YIELDY_TOKEN).rebase after epoch.distribute update

    function rebase() public {
        // we know about the issues surrounding block.timestamp, using it here will not cause any problems
        if (epoch.endTime <= block.timestamp) {
            uint256 balance = contractBalance();
            uint256 staked = IYieldy(YIELDY_TOKEN).totalSupply();

            if (balance <= staked) {
                epoch.distribute = 0;
            } else {
                epoch.distribute = balance - staked;
            }
            IYieldy(YIELDY_TOKEN).rebase(epoch.distribute, epoch.number);

            epoch.endTime = epoch.endTime + epoch.duration;
            epoch.timestamp = block.timestamp;
            epoch.number++;
        }
    }

Lines of code

https://github.com/code-423n4/2022-06-yieldy/blob/524f3b83522125fb7d4677fa7a7e5ba5a2c0fe67/src/contracts/Staking.sol#L674-L696

Vulnerability details

Impact

In the Yieldy contract, functions such as balanceOf/creditsForTokenBalance/tokenBalanceForCredits/transfer/transferFrom/burn/mint will use the rebasingCreditsPerToken variable, so before calling these functions in the Staking contract, make sure that the rebase of this epoch has occurred. Therefore, the rebase function should also be called in the unstake/claim/claimWithdraw function of the Staking contract.

Proof of Concept

https://github.com/code-423n4/2022-06-yieldy/blob/524f3b83522125fb7d4677fa7a7e5ba5a2c0fe67/src/contracts/Staking.sol#L674-L696 https://github.com/code-423n4/2022-06-yieldy/blob/524f3b83522125fb7d4677fa7a7e5ba5a2c0fe67/src/contracts/Staking.sol#L465-L508

Tools Used

None

Recommended Mitigation Steps

    function claim(address _recipient) public {
        Claim memory info = warmUpInfo[_recipient];
+      rebase();
...
    function claimWithdraw(address _recipient) public {
        Claim memory info = coolDownInfo[_recipient];
+      rebase();
...
    function unstake(uint256 _amount, bool _trigger) external {
        // prevent unstaking if override due to vulnerabilities asdf
        require(!isUnstakingPaused, "Unstaking is paused");
-        if (_trigger) {
            rebase();
-        }

Lines of code

https://github.com/code-423n4/2022-06-yieldy/blob/524f3b83522125fb7d4677fa7a7e5ba5a2c0fe67/src/contracts/Staking.sol#L167-L170

Vulnerability details

Impact

The owner can set affiliateFee to 10000 in the setAffiliateFee function of the Staking contract, which may frontrun the claimFromToken function.

Proof of Concept

https://github.com/code-423n4/2022-06-yieldy/blob/524f3b83522125fb7d4677fa7a7e5ba5a2c0fe67/src/contracts/Staking.sol#L167-L170

Tools Used

None

Recommended Mitigation Steps

Consider limiting affiliateFee in setAffiliateFee function