Missing approve before transferring of WETH to the recipient

Summary

Vulnerability Detail

In the _transferETHAndWrapIfFailWithGasLimit function, if the original transfer fails, it should wrap the ETH into WETH and transfer the WETH to the recipient.

Firstly, the amount of ETH is deposited into the WETH contract and then transferred to the recipient. The depositing of ETH will be successful, but the transfer will revert because msg.sender has not approved the transfer of the amount.

When the transfer() function of the WETH contract is called, it directly calls the transferFrom function, which requires approval for the tokens before to be to be transferred.

https://etherscan.io/token/0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2#code

 function transfer(address dst, uint wad) public returns (bool) {
        return transferFrom(msg.sender, dst, wad);
    }

    function transferFrom(address src, address dst, uint wad)
        public
        returns (bool)
    {
        require(balanceOf[src] >= wad);

        if (src != msg.sender && allowance[src][msg.sender] != uint(-1)) {
            require(allowance[src][msg.sender] >= wad);
            allowance[src][msg.sender] -= wad;
        }

        balanceOf[src] -= wad;
        balanceOf[dst] += wad;

        Transfer(src, dst, wad);

        return true;
    }

LowLevelWETH is not within the scope of the audit, but this will affect every part of the codebase where _transferETHAndWrapIfFailWithGasLimit() is used.

Also, if the original transfer fails because the gas is not enough, depositing and transferring WETH may not be possible.