MariaDB, as well as MySQL, is certainly a very useful resource to have at your disposal. However, it can also be used against you if configured improperly. Thankfully, it's not too hard to secure, but there are several points of consideration to make regarding your database server when developing your security design.
The first point is probably obvious to most of you, but I'll mention it just in case. Your database server should not be reachable from the Internet. I do understand that there are some edge cases when developing a network, and certain applications may require access to a MySQL database over the Internet. However, if your database server is accessible over the Internet, miscreants will try their best to attack it and gain entry. If there's any vulnerability in your version of MariaDB or MySQL, they'll most likely be able to hack into it.
In most organizations, a great way to implement a database server is to make it accessible by only internal servers....