More than 135 million cable modems around the world are vulnerable to a flaw that can be exploited remotely to knock them offline by cutting off the Internet access. Arris does not provide any password authentication set up on the modem’s user interface, thus allowing any local attacker to access the administration web interface at 192.168.100.1 without the need to enter a username and password. By clicking ‘Restart Cable Modem’ manually will disable victim’s modem for 2 to 3 minutes and every device on that network will lose access to the Internet.
Source: https://thehackernews.com/2016/04/hack-modem-internet.html