6.1.3 Making MySQL Secure Against Attackers
When you connect to a MySQL server, you should use a password. The password is not transmitted as cleartext over the connection. Password handling during the client connection sequence was upgraded in MySQL 4.1.1 to be very secure. If you are still using pre-4.1.1-style passwords, the encryption algorithm is not as strong as the newer algorithm. With some effort, a clever attacker who can sniff the traffic between the client and the server can crack the password. (See Section 18.104.22.168, “Password Hashing in MySQL”, for a discussion of the different password handling methods.)
All other information is transferred as text, and can be read by anyone who is able to watch the connection. If the connection between the client and the server goes through an untrusted network, and you are concerned about this, you can use the compressed protocol to make traffic much more difficult to decipher. You can also use MySQL's internal SSL support to make the connection even more secure. See Section 6.3, “Using Encrypted Connections”. Alternatively, use SSH to get an encrypted TCP/IP connection between a MySQL server and a MySQL client. You can find an Open Source SSH client at http://www.openssh.org/ , and a comparison of both Open Source and Commercial SSH clients at http://en.wikipedia.org/wiki/Comparison_of_SSH_clients .
To make a MySQL system secure, you should strongly consider the following suggestions:
Require all MySQL accounts to have a password. A client program does not necessarily know the identity of the person running it. It is common for client/server applications that the user can specify any user name to the client program. For example, anyone can use the mysql program to connect as any other person simply by invoking it as
other_userhas no password. If all accounts have a password, connecting using another user's account becomes much more difficult.
For a discussion of methods for setting passwords, see Section 6.2.10, “Assigning Account Passwords”.
Make sure that the only Unix user account with read or write privileges in the database directories is the account that is used for running mysqld.
Never run the MySQL server as the Unix
rootuser. This is extremely dangerous, because any user with the
FILEprivilege is able to cause the server to create files as
~root/.bashrc). To prevent this, mysqld refuses to run as
rootunless that is specified explicitly using the
mysqld can (and should) be run as an ordinary, unprivileged user instead. You can create a separate Unix account named
mysqlto make everything even more secure. Use this account only for administering MySQL. To start mysqld as a different Unix user, add a
useroption that specifies the user name in the
[mysqld]group of the
my.cnfoption file where you specify server options. For example:
This causes the server to start as the designated user whether you start it manually or by using mysqld_safe or mysql.server. For more details, see Section 6.1.5, “How to Run MySQL as a Normal User”.
Running mysqld as a Unix user other than
rootdoes not mean that you need to change the
rootuser name in the
usertable. User names for MySQL accounts have nothing to do with user names for Unix accounts.
Do not grant the
FILEprivilege to nonadministrative users. Any user that has this privilege can write a file anywhere in the file system with the privileges of the mysqld daemon. This includes the server's data directory containing the files that implement the privilege tables. To make
FILE-privilege operations a bit safer, files generated with
SELECT ... INTO OUTFILEdo not overwrite existing files and are writable by everyone.
FILEprivilege may also be used to read any file that is world-readable or accessible to the Unix user that the server runs as. With this privilege, you can read any file into a database table. This could be abused, for example, by using
LOAD DATAto load
/etc/passwdinto a table, which then can be displayed with
Do not grant the
SUPERprivilege to nonadministrative users. The output of mysqladmin processlist and
SHOW PROCESSLISTshows the text of any statements currently being executed, so any user who is permitted to see the server process list might be able to see statements issued by other users such as
UPDATE user SET password=PASSWORD('not_secure').
SUPERprivilege can be used to terminate client connections, change server operation by changing the value of system variables, and control replication servers.
Do not permit the use of symlinks to tables. (This capability can be disabled with the
--skip-symbolic-linksoption.) This is especially important if you run mysqld as
root, because anyone that has write access to the server's data directory then could delete any file in the system! See Section 22.214.171.124, “Using Symbolic Links for MyISAM Tables on Unix”.
Stored programs and views should be written using the security guidelines discussed in Section 23.6, “Stored Object Access Control”.
If you do not trust your DNS, you should use IP addresses rather than host names in the grant tables. In any case, you should be very careful about creating grant table entries using host name values that contain wildcards.
If you want to restrict the number of connections permitted to a single account, you can do so by setting the
max_user_connectionsvariable in mysqld. The
ALTER USERstatements also support resource control options for limiting the extent of server use permitted to an account. See Section 126.96.36.199, “CREATE USER Statement”, and Section 188.8.131.52, “ALTER USER Statement”.
If the plugin directory is writable by the server, it may be possible for a user to write executable code to a file in the directory using
SELECT ... INTO DUMPFILE. This can be prevented by making
plugin_dirread only to the server or by setting
secure_file_privto a directory where
SELECTwrites can be made safely.