Description

When the user calls the lock function to transfer ERC-20 tokens to the bridge on the Ethereum network, a Lock event is emitted. The backend observes this event or transaction to allow the user to receive funds on the Mina network.

In the current implementation, the return value of the ERC-20 transferFrom call is not checked.

function lock(address token, string memory receipt, uint256 amount) public payable {
    require(whitelistTokens[token], "Bridge: token must be in whitelist");
    require(amount <= maxAmount && amount >= minAmount, "Bridge: invalid amount");
    string memory name = "ETH";
    if (token == address(0)) {
        require(msg.value == amount, "Bridge: invalid amount");
    } else {
        IERC20(token).transferFrom(msg.sender, address(this), amount);
        name = IERC20(token).name();
    }
    emit Lock(msg.sender, receipt, token, amount, name);
}

Impact

There are tokens that comply with the ERC-20 standard but are implemented in a way that does not revert when a transfer fails. In such cases, the bridge may not receive the tokens, but the Lock event is still emitted. If a malicious user exploits this, they could inflate their funds on the Mina network and potentially drain the protocol.

Recommendations

Use the safeTransferFrom function from OpenZepplin's SafeERC20 library to ensure that the transfer is successful and handles potential errors properly.

Remediation

This issue has been acknowledged by Sotatek, and a fix was implemented in commit 17162c1a↗.