Decent - 0xJaeger's results

Lines of code

https://github.com/code-423n4/2024-01-decent/blob/main/src/UTB.sol#L259-L274

Vulnerability details

Impact

UTB.bridgeAndExecute() is used to execute a cross-chain transaction for the users from the host chain.

The issue is that the refund address that is passed as part of the bridgeInstructions struct is the msg.sender on the host chain as confirmed by the developers and in the natspec in the transaction executing contract UTBExecutor.sol.

This will be a problem if the msg.sender is a multisig wallet contract as the wallet holders might not have control over the same address in the destination chain, causing the received tokens to be lost.

In the worst case, the tokens could be sent to an undeployed address and an attacker could seize the opportunity to possibly steal the tokens by taking control of the refund address on the destination chain. (see Wintermute hack article)

Proof of Concept

https://github.com/code-423n4/2024-01-decent/blob/main/src/UTBExecutor.sol#L41-L82

function execute(
        address target,
        address paymentOperator,
        bytes memory payload,
        address token,
        uint amount,
        address payable refund,
        uint extraNative
    ) public onlyOwner {
        bool success;
        if (token == address(0)) {
            (success, ) = target.call{value: amount}(payload);
            if (!success) {
                (refund.call{value: amount}(""));
            }
            return;
        }

        uint initBalance = IERC20(token).balanceOf(address(this));

        IERC20(token).transferFrom(msg.sender, address(this), amount);
        IERC20(token).approve(paymentOperator, amount);

        if (extraNative > 0) {
            (success, ) = target.call{value: extraNative}(payload);
            if (!success) {
                (refund.call{value: extraNative}(""));
            }
        } else {
            (success, ) = target.call(payload);
        }

        uint remainingBalance = IERC20(token).balanceOf(address(this)) -
            initBalance;

        if (remainingBalance == 0) {
            return;
        }

        IERC20(token).transfer(refund, remainingBalance);
    }

Tools Used

Manual Analysis

Recommended Mitigation Steps

Provide the user with the ability to provide a custom refund address on the destination chain, so that multisig wallet owners can provide their address on the destination chain.

Assessed type

Other