Having MySQL using auth_socket as default authentication mechanism for the root user scares me, so I change it to password authentication with rigid controls on password quality and documentation.
If a user manage to have root access to this linux machine that has a MySQL database but doesn't have the password to log in into the service, he still can copy/modify/destroy the data?
The root user will have access to, at the very least, the database file that is stored on the computer. This means reguardless of how the service is configured they can copy and delete the data. If your databse is not encrypted by some means he will be able to modify the data too.
root have access to every single file.
Commented
Jul 10, 2018 at 15:03
You obviously know the answer now: yes. However, it is even easier than it seems. As a root user you can actually reset the root password for a MySQL installation. I've had to do this before: I had a brand new installation and I forgot to record the MySQL root password. It took less than 5 minutes to reset the root password in MySQL, and I had full access to the MySQL database after doing so - it made no changes to anything in MySQL at all (other than the root password).
Of course even that might not matter. If your database server and application server are one machine then a smart attacker can just look at your application, see how it is authenticating (typically as simple as reading credentials out of source code or an environment configuration), and login like that.
It would be very difficult to come up with a way to lock the root user out of MySQL, and if you managed to do it you would probably be more likely to hurt yourself than a malicious user. In general if an unauthorized user gains root access to your server, you're pretty much hosed.
