Database administrators should use the following guidelines to keep passwords secure.
MySQL stores passwords for user accounts in the
mysql.user table. Access to this table should
never be granted to any nonadministrative accounts.
A user who has access to modify the plugin directory (the value
of the plugin_dir system
variable) or the my.cnf file that specifies
the location of the plugin directory can replace plugins and
modify the capabilities provided by plugins.
Passwords can appear as plain text in SQL statements such as
CREATE USER,
GRANT, and
SET PASSWORD, or statements that
invoke the PASSWORD() function.
If these statements are logged by the MySQL server, the
passwords become available to anyone with access to the logs.
This applies to the general query log, the slow query log, and
the binary log (see Section 5.2, “MySQL Server Logs”). To guard
against unwarranted exposure to log files, they should be
located in a directory that restricts access to only the server
and the database administrator. If you log to tables in the
mysql database, access to the tables should
never be granted to any nonadministrative accounts.
Replication slaves store the password for the replication master
in the master.info file. Access to this
file should be restricted to the database adminstrator.
Database backups that include tables or log files containing passwords should be protected using a restricted access mode.