Users have the ability to stake $YEET tokens in the StakeV2.sol contract in order to get rewards.
At any point, a user is allowed to unstake his tokens which will be submitted to a vesting period of 10 days. The vested amount of tokens will be claimable and effectively unstaked after this period has passed.
Contract managers can execute the distribution of $YEET rewards which will distribute the excess of tokens across all stakers.
This excess is wrongly calculated and includes the vested tokens users are trying to unstake.
Vulnerability details
The number of tokens users have staked in the contract is accounted in the totalSupply variable. This number is increased everytime a user stakes and everytime a user starts the unstake process.
function stake(uint256 amount) external {
require(amount > 0, "Amount must be greater than 0");
_updateRewards(msg.sender);
stakingToken.transferFrom(msg.sender, address(this), amount);
balanceOf[msg.sender] += amount;
@> totalSupply += amount;
emit Stake(msg.sender, amount);
}
function startUnstake(uint256 unStakeAmount) external {
require(unStakeAmount > 0, "Amount must be greater than 0");
require(stakedTimes[msg.sender] < STAKING_LIMIT, "Amount must be less then the STAKING_LIMIT constant"); // DOS protection https://github.com/Enigma-Dark/Yeet/issues/12
_updateRewards(msg.sender);
uint256 amount = balanceOf[msg.sender];
require(amount >= unStakeAmount, "Insufficient balance");
balanceOf[msg.sender] -= unStakeAmount;
@> totalSupply -= unStakeAmount;
uint256 start = block.timestamp;
uint256 end = start + VESTING_PERIOD;
vestings[msg.sender].push(Vesting(unStakeAmount, start, end));
stakedTimes[msg.sender]++;
emit VestingStarted(msg.sender, unStakeAmount, vestings[msg.sender].length - 1);
}
The function involved when calculating the rewards to distribute subtracts the $YEET token balance of the contract with the totalSupply.
function accumulatedDeptRewardsYeet() public view returns (uint256) {
@> return stakingToken.balanceOf(address(this)) - totalSupply;
}
/// @notice The function used to distribute excess rewards to the vault.
function executeRewardDistributionYeet(
IZapper.SingleTokenSwap calldata swap,
IZapper.KodiakVaultStakingParams calldata stakingParams,
IZapper.VaultDepositParams calldata vaultParams
) external onlyManager nonReentrant {
@> uint256 accRevToken0 = accumulatedDeptRewardsYeet();
require(accRevToken0 > 0, "No rewards to distribute");
require(swap.inputAmount <= accRevToken0, "Insufficient rewards to distribute");
stakingToken.approve(address(zapper), accRevToken0);
IERC20 token0 = IKodiakVaultV1(stakingParams.kodiakVault).token0();
IERC20 token1 = IKodiakVaultV1(stakingParams.kodiakVault).token1();
uint256 vaultSharesMinted;
require(
address(token0) == address(stakingToken) || address(token1) == address(stakingToken),
"Neither token0 nor token1 match staking token"
);
if (address(token0) == address(stakingToken)) {
(, vaultSharesMinted) = zapper.zapInToken0(swap, stakingParams, vaultParams);
} else {
(, vaultSharesMinted) = zapper.zapInToken1(swap, stakingParams, vaultParams);
}
_handleVaultShares(vaultSharesMinted);
emit RewardsDistributedToken0(accRevToken0, rewardIndex);
}
Thus, the resulting amount of rewards fail to account for the vested amount of tokens waiting to be unstaked.
This means when the vesting period has ended, a user might not be able to claim his tokens because the contract does not have enough liquidity.
Impact
Users might be prevented from withdrawing their tokens after unstaking them.
Proof of Concept
Proof of concept
Alice stakes 800 tokens: totalSupply == 800
The Yeet game is being played and 1000 tokens are accrued as rewards: stakingToken.balanceOf(address(this)) == 1800
Alice wants to unstake her 800 tokens so she starts the vesting period to claim them 10 days later: totalSupply == 800 - 800 == 0
Manager distributes the maximum amount of rewards possible: stakingToken.balanceOf(address(this)) - totalSupply meaning 1800 - 0 == 1800
When Alice attempts to unstake her 800 tokens, the transaction will fail because the contract
Recommendation
Maintain a storage variable vestedTokens that accounts for the vested amount of $YEET and increases everytime a user startUnstake() and decreases when a user unstake().
Modify the accumulatedDeptRewardsYeet() to account for the vested tokens.
function accumulatedDeptRewardsYeet() public view returns (uint256) {
- return stakingToken.balanceOf(address(this)) - totalSupply;
+ return stakingToken.balanceOf(address(this)) - totalSupply + vestedTokens;
}
