By default, MariaDB is not hardened. You can secure MariaDB using the mysql_secure_installation script. You should read and below each steps carefully which will set root password, remove anonymous users, disallow remote root login, and remove the test database and access to secure MariaDB.
For the record, those that are not familiar with Linux may not be familiar with man. I only know of it's existence, but trying to figure out how to use it would require a google adventure in and of itself. Possibly a worthwhile venture, but you should realize that I found THIS VERY post via google and it answered the EXACT question I was asking. Resources, my friend. Resources are invaluable. And you may think this was pointless and that he should have just checked the man, but this has helped me and HUNDREDS of others (thousand even). So please consider that.