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MySQL Cluster :: 5 Management of MySQL Cluster :: 5.9 MySQL Cluster Security Issues :: 5.9.2 MySQL Cluster and MySQL Privileges
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5.9.2. MySQL Cluster and MySQL Privileges

In this section, we discuss how the MySQL privilege system works in relation to MySQL Cluster and the implications of this for keeping a MySQL Cluster secure.

Standard MySQL privileges apply to MySQL Cluster tables. This includes all MySQL privilege types (SELECT privilege, UPDATE privilege, DELETE privilege, and so on) granted on the database, table, and column level. As with any other MySQL Server, user and privilege information is stored in the mysql system database. The SQL statements used to grant and revoke privileges on NDB tables, databases containing such tables, and columns within such tables are identical in all respects with the GRANT and REVOKE statements used in connection with database objects involving any (other) MySQL storage engine. The same thing is true with respect to the CREATE USER and DROP USER statements.

It is important to keep in mind that the MySQL grant tables use the MyISAM storage engine. Because of this, those tables are not duplicated or shared among MySQL servers acting as SQL nodes in a MySQL Cluster. By way of example, suppose that two SQL nodes A and B are connected to the same MySQL Cluster, which has an NDB table named mytable in a database named mydb, and that you execute an SQL statement on server A that creates a new user jon@localhost and grants this user the SELECT privilege on that table: 

mysql> GRANT SELECT ON mydb.mytable
    ->   TO jon@localhost IDENTIFIED BY 'mypass';

This user is not created on server B. In order for this to take place, the statement must also be run on server B. Similarly, statements run on server A and affecting the privileges of existing users on server A do not affect users on server B unless those statements are actually run on server B as well.

In other words, changes in users and their privileges do not automatically propagate between SQL nodes. Synchronization of privileges between SQL nodes must be done either manually or by scripting an application that periodically synchronizes the privilege tables on all SQL nodes in the cluster.

Conversely, because there is no way in MySQL to deny privileges (privileges can either be revoked or not granted in the first place, but not denied as such), there is no special protection for NDB tables on one SQL node from users that have privileges on another SQL node. The most far-reaching example of this is the MySQL root account, which can perform any action on any database object. In combination with empty [mysqld] or [api] sections of the config.ini file, this account can be especially dangerous. To understand why, consider the following scenario:

  • The config.ini file contains at least one empty [mysqld] or [api] section. This means that the Cluster management server performs no checking of the host from which a MySQL Server (or other API node) accesses the MySQL Cluster.

  • There is no firewall, or the firewall fails to protect against access to the Cluster from hosts external to the network.

  • The host name or IP address of the Cluster's management server is known or can be determined from outside the network.

If these conditions are true, then anyone, anywhere can start a MySQL Server with --ndbcluster --ndb-connectstring=management_host and access the Cluster. Using the MySQL root account, this person can then perform the following actions:

  • Execute a SHOW DATABASES statement to obtain a list of all databases that exist in the cluster

  • Execute a SHOW TABLES FROM some_database statement to obtain a list of all NDB tables in a given database

  • Run any legal MySQL statements on any of those tables, such as:

    • SELECT * FROM some_table to read all the data from any table

    • DELETE FROM some_table to delete all the data from a table

    • DESCRIBE some_table or SHOW CREATE TABLE some_table to determine the table schema

    • UPDATE some_table SET column1 = any_value1 to fill a table column with “garbage” data; this could actually cause much greater damage than simply deleting all the data

      Even more insidious variations might include statements like these: 

      UPDATE some_table SET an_int_column = an_int_column + 1

      or 

      UPDATE some_table SET a_varchar_column = REVERSE(a_varchar_column)

      Such malicious statements are limited only by the imagination of the attacker.

    The only tables that would be safe from this sort of mayhem would be those tables that were created using storage engines other than NDB, and so not visible to a “rogue” SQL node.

    Note

    A user who can log in as root can also access the INFORMATION_SCHEMA database and its tables, and so obtain information about databases, tables, stored routines, scheduled events, and any other database objects for which metadata is stored in INFORMATION_SCHEMA.

    It is also a very good idea to use different passwords for the root accounts on different cluster SQL nodes.

In sum, you cannot have a safe MySQL Cluster if it is directly accessible from outside your local network.

Important

Never leave the MySQL root account password empty. This is just as true when running MySQL as a MySQL Cluster SQL node as it is when running it as a standalone (non-Cluster) MySQL Server, and should be done as part of the MySQL installation process before configuring the MySQL Server as an SQL node in a MySQL Cluster.

You should never convert the system tables in the mysql database to use the NDB storage engine. There are a number of reasons why you should not do this, but the most important reason is this: Many of the SQL statements that affect mysql tables storing information about user privileges, stored routines, scheduled events, and other database objects cease to function if these tables are changed to use any storage engine other than MyISAM. This is a consequence of various MySQL Server internals which are not expected to change in the foreseeable future.

If you need to synchronize mysql system tables between SQL nodes, you can use standard MySQL replication to do so, or employ a script to copy table entries between the MySQL servers.

Summary.  The two most important points to remember regarding the MySQL privilege system with regard to MySQL Cluster are:

  1. Users and privileges established on one SQL node do not automatically exist or take effect on other SQL nodes in the cluster.

    Conversely, removing a user or privilege on one SQL node in the cluster does not remove the user or privilege from any other SQL nodes.

  2. Once a MySQL user is granted privileges on an NDB table from one SQL node in a MySQL Cluster, that user can “see” any data in that table regardless of the SQL node from which the data originated.