Is rooting android dangerous

Rooting itself is not dangreous but what you do with it can be. Like for example if you wanted to flash a custom ROM or a custom recovery it is dangreous cause you could possibly brick your phone if not done correctly. But just rooting the phone no. But to warn you it does void your warranty. The only way to fix that is to install the offical firmware back and make sure nothing is modified in the system but if the KNOX is tampered with then no it will void your warranty completely.