erc20 contract KoreaShow bug(CVE-2018-10973)

An integer overflow in the transferMulti function of a smart contract
implementation for KoreaShow, an Ethereum ERC20 token, allows attackers to
accomplish an unauthorized increase of digital assets via crafted _value
parameters.

Let`s see where this issue is:

function transferMulti(address[] _to, uint256[] _value) public returns
(uint256 amount){

        require(_to.length == _value.length);

        uint8 len = uint8(_to.length);

        for(uint8 j; j<len; j++){

            amount += _value[j]; <------here, crafted _value can make
amount overflow

        }

        require(balanceOf[msg.sender] >= amount);

        for(uint8 i; i<len; i++){

            address _toI = _to[i];

            uint256 _valueI = _value[i];

            balanceOf[_toI] += _valueI;

            balanceOf[msg.sender] -= _valueI;

            Transfer(msg.sender, _toI, _valueI);

        }

    }