6.2.10 Password Expiration and Sandbox Mode

MySQL 5.6 introduces password-expiration capability, which enables database administrators to require that users reset their password. The immediately following discussion describes how password expiration works currently. Later, the development of this capability is detailed as it occurred over several versions, as background to help you understand what features are available when. However, to ensure that you can take advantage of all features and fixes, you should use the most recent available version of MySQL if possible.

How Password Expiration Works

To expire an account password, use the ALTER USER statement. For example:

ALTER USER 'myuser'@'localhost' PASSWORD EXPIRE;

For each connection that uses an account with an expired password, the server either disconnects the client or restricts the client to “sandbox mode,” in which the server permits to the client only those operations necessary to reset the expired password. Which action is taken by the server depends on both client and server settings, as discussed later.

If the server disconnects the client, it returns an ER_MUST_CHANGE_PASSWORD_LOGIN error:

shell> mysql -u myuser -p
Password: ******
ERROR 1862 (HY000): Your password has expired. To log in you must
change it using a client that supports expired passwords.

If the server restricts the client to sandbox mode, these operations are permitted within the client session:

• The client can reset the account password with SET PASSWORD. After the password has been reset, the server restores normal access for the session, as well as for subsequent connections that use the account.

  It is possible to “reset” a password by setting it to its current value. As a matter of good policy, it is preferable to choose a different password.

• The client can use SET statements. This might be necessary prior to resetting the password; for example, if the account password uses a hashing format that requires the old_passwords system variable to be set to a value different from its default.

For any operation not permitted within the session, the server returns an ER_MUST_CHANGE_PASSWORD error:

mysql> USE performance_schema;
ERROR 1820 (HY000): You must SET PASSWORD before executing this statement

mysql> SELECT 1;
ERROR 1820 (HY000): You must SET PASSWORD before executing this statement

That is what normally happens for interactive invocations of the mysql client because by default such invocations are put in sandbox mode. To clear the error and resume normal functioning, select a new password.

For noninteractive invocations of the mysql client (for example, in batch mode), the server normally disconnects the client if the password is expired. To permit noninteractive mysql invocations to stay connected so that the password can be changed (using the statements just described), add the --connect-expired-password option to the mysql command.

As mentioned previously, whether the server disconnects an expired-password client or restricts it to sandbox mode depends on a combination of client and server settings. The following discussion describes the relevant settings and how they interact. The discussion applies only for accounts with expired passwords. If a client connects using a nonexpired password, the server handles the client normally.

On the client side, a given client indicates whether it can handle sandbox mode for expired passwords. For clients that use the C client library, there are two ways to do this:

• Pass the MYSQL_OPT_CAN_HANDLE_EXPIRED_PASSWORDS flag to mysql_options() prior to connecting:

  arg = 1;
  result = mysql_options(mysql,
                         MYSQL_OPT_CAN_HANDLE_EXPIRED_PASSWORDS,
                         &arg);

  The mysql client enables MYSQL_OPT_CAN_HANDLE_EXPIRED_PASSWORDS if invoked interactively or the --connect-expired-password option is given.

• Pass the CLIENT_CAN_HANDLE_EXPIRED_PASSWORDS flag to mysql_real_connect() at connection time:

  mysql = mysql_real_connect(mysql,
                             host, user, password, db,
                             port, unix_socket,
                             CLIENT_CAN_HANDLE_EXPIRED_PASSWORDS);

Other MySQL Connectors have their own conventions for indicating readiness to handle sandbox mode. See the documentation for the Connector in which you are interested.

On the server side, if a client indicates that it can handle expired passwords, the server puts it in sandbox mode.

If a client does not indicate that it can handle expired passwords (or uses an older version of the client library that cannot so indicate), the server action depends on the value of the disconnect_on_expired_password system variable:

• If disconnect_on_expired_password is enabled (the default), the server disconnects the client with an ER_MUST_CHANGE_PASSWORD_LOGIN error.

• If disconnect_on_expired_password is disabled, the server puts the client in sandbox mode.

The preceding client and server settings apply only for accounts with expired passwords. If a client connects using a nonexpired password, the server handles the client normally.

Development of Password-Expiration Capability

The following timeline describes the versions in which various password-expiration features were added.

• MySQL 5.6.6: Initial implementation of password expiration.

  The password_expired column is introduced in the mysql.user system table to enable DBAs to expire account passwords. The column default value is 'N' (not expired).

  The ALTER USER statement is introduced as the SQL interface for setting the password_expired column to 'Y'.

  Connections that use an account with an expired password enter “sandbox mode” that permits only SET PASSWORD statements. For other statements, the server returns an ER_MUST_CHANGE_PASSWORD error. The intent is to force the client to reset the password before the server permits any other operations. SET PASSWORD resets the account password and sets password_expired to 'N'.

  A bug in the initial implementation is that ALTER USER sets the Password column in the mysql.user system table to the empty string. The implication is that users should wait until MySQL 5.6.7 to use this statement.

• MySQL 5.6.7: ALTER USER is fixed to not set the Password column to the empty string.

• MySQL 5.6.8: ALTER USER can be used as a prepared statement.

  mysqladmin password is made capable of setting passwords for accounts with expired native or old-native passwords.

  Sandbox mode is changed to permit clients to execute SET statements in addition to SET PASSWORD Prohibiting SET prevented clients that needed to set old_passwords from resetting their password. It also broke some Connectors, which use SET extensively at connect time to initialize the session environment.

• MySQL 5.6.9: Sandbox mode is changed to permit SET PASSWORD only if the account named in the statement matches the account the client authenticated as.

• MySQL 5.6.10: Sandbox mode is changed to permit better control over how the server handles client connections for accounts with expired passwords, and to permit clients to signal whether they are capable of handling expired passwords:

  • The disconnect_on_expired_password system variable is added, which controls how the server treats expired-password accounts.

  • Two flags are added to the C API client library: MYSQL_OPT_CAN_HANDLE_EXPIRED_PASSWORDS for mysql_options() and CLIENT_CAN_HANDLE_EXPIRED_PASSWORDS for mysql_real_connect(). Each flag enables a client program to indicate whether it can handle sandbox mode for accounts with expired passwords.

    MYSQL_OPT_CAN_HANDLE_EXPIRED_PASSWORDS is enabled for mysqltest unconditionally, for mysql in interactive mode, and for mysqladmin if the first command is password.

  • The ER_MUST_CHANGE_PASSWORD_LOGIN error is added. The server returns this error when it disconnects a client.

  • MySQL 5.6.12: The --connect-expired-password option is added to the mysql client to enable password-change statement execution in batch mode for accounts with an expired password.

Concurrent with these changes to sandbox mode in MySQL Server and the C API client library, work begins to modify Connectors for conformance to the changes.