// Bridge.sol - Vulnerable bridge contract
contract Bridge {
    mapping(bytes32 => bool) public processed;
    event Deposited(address from, address to, uint256 amount, uint256 chainId);
    function deposit(address to, uint256 amount, uint256 chainId) external payable {
        emit Deposited(msg.sender, to, amount, chainId);
    }
    function withdraw(bytes memory proof, address from, address to, uint256 amount, uint256 chainId) external {
        // Verify proof signature (simulated)
        require(verifyProof(proof, from, to, amount, chainId), "Invalid proof");
        // Missing check: did this message originate from chainId?
        // An attacker can replay a Deposit event from another chain where they are the 'from'
        payable(to).transfer(amount);
    }
    function verifyProof(...) internal pure returns (bool) { return true; } // simplified
}