The TYPO3 database contains all data of backend and frontend users and therefore special care must be taken not to grant unauthorized access.
Secure passwords, usernames and minimum access privileges¶
The MySQL privilege system authenticates a (database-)user who connects from the TYPO3 host (which is possibly on the same machine) and associates that user with privileges on a database. These privileges are for example: SELECT, INSERT, UPDATE, DELETE, etc.
When creating this user, follow the guidelines for secure passwords in this document. The name of the user should definitely not be "root", "admin", "typo3", etc. You should create a database specific user with limited privileges for accessing the database from TYPO3. Usually this user does not require access to any other databases and the database of your TYPO3 instance should usually only have one associated database user.
MySQL and other database systems provide privileges that apply at different levels of operation. It depends on your individual system and setup which privileges the database user needs (SELECT, INSERT, UPDATE and some more are essential of course) but privileges like LOCK TABLES, FILE, PROCESS, CREATE USER, RELOAD, SHUTDOWN, etc. are in the context of administrative privileges and not required in most cases.
See the documentation of your database system on how to set up database users and access privileges (e.g. chapter 5.4 and chapter 12.7.1 of the MySQL documentation).
Disallow external access¶
The database server should only be reachable from the server that your TYPO3 installation is running on. Make sure to disable any access from outside of your server or network (settings in firewall rules) and/or do not bind the database server to a network interface.
If you are using MySQL, read the chapter "Server Options" in the manual and check for the "skip-networking" and "bind-address" options in particular.
Database administration tools¶
phpMyAdmin and similar tools intend to allow the administration of MySQL database servers over the Web. Under certain circumstances, it might be required to access the database "directly", during a project development phase for example. Tools like "phpMyAdmin" (also available as a TYPO3 extension by the way) cause extra effort for ongoing maintenance (regular updates of these tools are required to ensure a minimum level of security). If they are not avoidable by any chance, the standalone version with an additional web server's access authentication (e.g. Apache's ".htaccess" mechanism) should be used at least.
However, due to the fact that a properly configured TYPO3 system does not require direct access to the database for editors or TYPO3 integrators, those applications should not be used on a production site at all.