Thursday, 5 December 2019

Privileges Provided by MySQL

The privileges granted to a MySQL account determine which operations the account can perform. MySQL privileges differ in the contexts in which they apply and at different levels of operation:
  • Administrative privileges enable users to manage operation of the MySQL server. These privileges are global because they are not specific to a particular database.
  • Database privileges apply to a database and to all objects within it. These privileges can be granted for specific databases, or globally so that they apply to all databases.
  • Privileges for database objects such as tables, indexes, views, and stored routines can be granted for specific objects within a database, for all objects of a given type within a database (for example, all tables in a database), or globally for all objects of a given type in all databases.
Privileges also differ in terms of whether they are static (built in to the server) or dynamic (defined at runtime). Whether a privilege is static or dynamic affects its availability to be granted to user accounts and roles. For information about the differences between static and dynamic privileges, see Static Versus Dynamic Privileges.)
Information about account privileges is stored in the grant tables in the mysql system database. For a description of the structure and contents of these tables, see Section 6.2.3, “Grant Tables”. The MySQL server reads the contents of the grant tables into memory when it starts, and reloads them under the circumstances indicated in Section 6.2.13, “When Privilege Changes Take Effect”. The server bases access-control decisions on the in-memory copies of the grant tables.
Important
Some MySQL releases introduce changes to the grant tables to add new privileges or features. To make sure that you can take advantage of any new capabilities, update your grant tables to the current structure whenever you upgrade MySQL. See Section 2.11, “Upgrading MySQL”.
The following sections summarize the available privileges, provide more detailed descriptions of each privilege, and offer usage guidelines.

Summary of Available Privileges

The following table shows the static privilege names used in GRANT and REVOKE statements, along with the column name associated with each privilege in the grant tables and the context in which the privilege applies.
Table 6.2 Permissible Static Privileges for GRANT and REVOKE
PrivilegeGrant Table ColumnContext
ALL [PRIVILEGES]Synonym for “all privileges”Server administration
ALTERAlter_privTables
ALTER ROUTINEAlter_routine_privStored routines
CREATECreate_privDatabases, tables, or indexes
CREATE ROLECreate_role_privServer administration
CREATE ROUTINECreate_routine_privStored routines
CREATE TABLESPACECreate_tablespace_privServer administration
CREATE TEMPORARY TABLESCreate_tmp_table_privTables
CREATE USERCreate_user_privServer administration
CREATE VIEWCreate_view_privViews
DELETEDelete_privTables
DROPDrop_privDatabases, tables, or views
DROP ROLEDrop_role_privServer administration
EVENTEvent_privDatabases
EXECUTEExecute_privStored routines
FILEFile_privFile access on server host
GRANT OPTIONGrant_privDatabases, tables, or stored routines
INDEXIndex_privTables
INSERTInsert_privTables or columns
LOCK TABLESLock_tables_privDatabases
PROCESSProcess_privServer administration
PROXYSee proxies_priv tableServer administration
REFERENCESReferences_privDatabases or tables
RELOADReload_privServer administration
REPLICATION CLIENTRepl_client_privServer administration
REPLICATION SLAVERepl_slave_privServer administration
SELECTSelect_privTables or columns
SHOW DATABASESShow_db_privServer administration
SHOW VIEWShow_view_privViews
SHUTDOWNShutdown_privServer administration
SUPERSuper_privServer administration
TRIGGERTrigger_privTables
UPDATEUpdate_privTables or columns
USAGESynonym for “no privileges”Server administration

The following table shows the dynamic privilege names used in GRANT and REVOKE statements, along with the context in which the privilege applies.
Table 6.3 Permissible Dynamic Privileges for GRANT and REVOKE
PrivilegeContext
APPLICATION_PASSWORD_ADMINDual password administration
AUDIT_ADMINAudit log administration
BACKUP_ADMINBackup administration
BINLOG_ADMINBackup and Replication administration
BINLOG_ENCRYPTION_ADMINBackup and Replication administration
CLONE_ADMINClone administration
CONNECTION_ADMINServer administration
ENCRYPTION_KEY_ADMINServer administration
FIREWALL_ADMINFirewall administration
FIREWALL_USERFirewall administration
GROUP_REPLICATION_ADMINReplication administration
INNODB_REDO_LOG_ARCHIVERedo log archiving administration
NDB_STORED_USERNDB Cluster
PERSIST_RO_VARIABLES_ADMINServer administration
REPLICATION_APPLIERPRIVILEGE_CHECKS_USER for a replication channel
REPLICATION_SLAVE_ADMINReplication administration
RESOURCE_GROUP_ADMINResource group administration
RESOURCE_GROUP_USERResource group administration
ROLE_ADMINServer administration
SESSION_VARIABLES_ADMINServer administration
SET_USER_IDServer administration
SYSTEM_USERServer administration
SYSTEM_VARIABLES_ADMINServer administration
TABLE_ENCRYPTION_ADMINServer administration
VERSION_TOKEN_ADMINServer administration
XA_RECOVER_ADMINServer administration

Static Privilege Descriptions

Static privileges are built in to the server, in contrast to dynamic privileges, which are defined at runtime. The following list describes each static privilege available in MySQL.
Particular SQL statements might have more specific privilege requirements than indicated here. If so, the description for the statement in question provides the details.
  • These privilege specifiers are shorthand for “all privileges available at a given privilege level” (except GRANT OPTION). For example, granting ALL at the global or table level grants all global privileges or all table-level privileges, respectively.
  • Enables use of the ALTER TABLE statement to change the structure of tables. ALTER TABLE also requires the CREATE and INSERT privileges. Renaming a table requires ALTER and DROP on the old table, CREATE, and INSERT on the new table.
  • Enables use of statements that alter or drop stored routines (stored procedures and functions).
  • Enables use of statements that create new databases and tables.
  • Enables use of the CREATE ROLE statement. (The CREATE USER privilege also enables use of the CREATE ROLE statement.) See Section 6.2.10, “Using Roles”.
    The CREATE ROLE and DROP ROLE privileges are not as powerful as CREATE USER because they can be used only to create and drop accounts. They cannot be used as CREATE USER can be modify account attributes or rename accounts. See User and Role Interchangeability.
  • Enables use of statements that create stored routines (stored procedures and functions).
  • Enables use of statements that create, alter, or drop tablespaces and log file groups.
  • Enables the creation of temporary tables using the CREATE TEMPORARY TABLE statement.
    After a session has created a temporary table, the server performs no further privilege checks on the table. The creating session can perform any operation on the table, such as DROP TABLE, INSERT, UPDATE, or SELECT. For more information, see Section 13.1.20.3, “CREATE TEMPORARY TABLE Statement”.
  • Enables use of the ALTER USER, CREATE ROLE, CREATE USER, DROP ROLE, DROP USER, RENAME USER, and REVOKE ALL PRIVILEGES statements.
  • Enables use of the CREATE VIEW statement.
  • Enables rows to be deleted from tables in a database.
  • Enables use of statements that drop (remove) existing databases, tables, and views. The DROP privilege is required to use the ALTER TABLE ... DROP PARTITION statement on a partitioned table. The DROP privilege is also required for TRUNCATE TABLE.
  • Enables use of the DROP ROLE statement. (The CREATE USER privilege also enables use of the DROP ROLE statement.) See Section 6.2.10, “Using Roles”.
    The CREATE ROLE and DROP ROLE privileges are not as powerful as CREATE USER because they can be used only to create and drop accounts. They cannot be used as CREATE USER can be modify account attributes or rename accounts. See User and Role Interchangeability.
  • Enables use of statements that create, alter, drop, or display events for the Event Scheduler.
  • Enables use of statements that execute stored routines (stored procedures and functions).
  • Affects the following operations and server behaviors:
    • Enables reading and writing files on the server host using the LOAD DATA and SELECT ... INTO OUTFILE statements and the LOAD_FILE() function. A user who has the FILE privilege can read any file on the server host that is either world-readable or readable by the MySQL server. (This implies the user can read any file in any database directory, because the server can access any of those files.)
    • Enables creating new files in any directory where the MySQL server has write access. This includes the server's data directory containing the files that implement the privilege tables.
    • Enables use of the DATA DIRECTORY or INDEX DIRECTORY table option for the CREATE TABLE statement.
    As a security measure, the server does not overwrite existing files.
    To limit the location in which files can be read and written, set the secure_file_priv system variable to a specific directory. See Section 5.1.8, “Server System Variables”.
  • Enables you to grant to or revoke from other users those privileges that you yourself possess.
  • Enables use of statements that create or drop (remove) indexes. INDEX applies to existing tables. If you have the CREATE privilege for a table, you can include index definitions in the CREATE TABLE statement.
  • Enables rows to be inserted into tables in a database. INSERT is also required for the ANALYZE TABLE, OPTIMIZE TABLE, and REPAIR TABLE table-maintenance statements.
  • Enables use of explicit LOCK TABLES statements to lock tables for which you have the SELECT privilege. This includes use of write locks, which prevents other sessions from reading the locked table.
  • Enables display of information about the threads executing within the server (that is, information about the statements being executed by sessions). The privilege enables use of SHOW PROCESSLIST or mysqladmin processlist to see threads belonging to other accounts; you can always see your own threads. The PROCESS privilege also enables use of SHOW ENGINE.
  • Enables one user to impersonate or become known as another user. See Section 6.2.18, “Proxy Users”.
  • Creation of a foreign key constraint requires the REFERENCES privilege for the parent table.
  • Enables use of the FLUSH statement. It also enables mysqladmin commands that are equivalent to FLUSH operations: flush-hosts, flush-logs, flush-privileges, flush-status, flush-tables, flush-threads, refresh, and reload.
    The reload command tells the server to reload the grant tables into memory. flush-privileges is a synonym for reload. The refresh command closes and reopens the log files and flushes all tables. The other flush-xxx commands perform functions similar to refresh, but are more specific and may be preferable in some instances. For example, if you want to flush just the log files, flush-logs is a better choice than refresh.
    The RELOAD privilege also enables use of the RESET MASTER and RESET SLAVE statements.
  • Enables use of the SHOW MASTER STATUS, SHOW SLAVE STATUS, and SHOW BINARY LOGS statements. Grant this privilege to accounts that are used by slave servers to connect to the current server as their master.
  • Enables the account to request updates that have been made to databases on the master server, using the SHOW SLAVE HOSTS, SHOW RELAYLOG EVENTS, and SHOW BINLOG EVENTS statements. This privilege is also required to use the mysqlbinlog options --read-from-remote-server (-R) and --read-from-remote-master. Grant this privilege to accounts that are used by slave servers to connect to the current server as their master.
  • Enables rows to be selected from tables in a database. SELECT statements require the SELECT privilege only if they actually access tables. Some SELECT statements do not access tables and can be executed without permission for any database. For example, you can use SELECT as a simple calculator to evaluate expressions that make no reference to tables:
    SELECT 1+1;
SELECT PI()*2;
    The SELECT privilege is also needed for other statements that read column values. For example, SELECT is needed for columns referenced on the right hand side of col_name=expr assignment in UPDATE statements or for columns named in the WHERE clause of DELETE or UPDATE statements.
    The SELECT privilege is needed for tables or views used with EXPLAIN, including any underlying tables in view definitions.
  • Enables the account to see database names by issuing the SHOW DATABASE statement. Accounts that do not have this privilege see only databases for which they have some privileges, and cannot use the statement at all if the server was started with the --skip-show-database option.
    Caution
    Because any static global privilege is considered a privilege for all databases, any static global privilege enables a user to see all database names with SHOW DATABASES or by examining the SCHEMATA table of INFORMATION_SCHEMA, except databases that have been restricted at the database level by partial revokes.
  • Enables use of the SHOW CREATE VIEW statement. This privilege is also needed for views used with EXPLAIN.
  • Enables use of the SHUTDOWN and RESTART statements, the mysqladmin shutdown command, and the mysql_shutdown() C API function.
  • SUPER is a powerful and far-reaching privilege and should not be granted lightly. If an account needs to perform only a subset of SUPER operations, it may be possible to achieve the desired privilege set by instead granting one or more dynamic privileges, each of which confers more limited capabilities. See Dynamic Privilege Descriptions.
    Note
    SUPER is deprecated and will be removed in a future version of MySQL. See Migrating Accounts from SUPER to Dynamic Privileges.
    SUPER affects the following operations and server behaviors:
    • Enables system variable changes at runtime:
    • Enables changes to global transaction characteristics (see Section 13.3.7, “SET TRANSACTION Statement”).
      The corresponding dynamic privilege is SYSTEM_VARIABLES_ADMIN.
    • Enables the account to start and stop replication, including Group Replication.
      The corresponding dynamic privilege is REPLICATION_SLAVE_ADMIN for regular replication, GROUP_REPLICATION_ADMIN for Group Replication.
    • Enables use of the CHANGE MASTER TO and CHANGE REPLICATION FILTER statements.
      The corresponding dynamic privilege is REPLICATION_SLAVE_ADMIN.
    • Enables binary log control by means of the PURGE BINARY LOGS and BINLOG statements.
      The corresponding dynamic privilege is BINLOG_ADMIN.
    • Enables setting the effective authorization ID when executing a view or stored program. A user with this privilege can specify any account in the DEFINER attribute of a view or stored program.
      The corresponding dynamic privilege is SET_USER_ID.
    • Enables use of the CREATE SERVER, ALTER SERVER, and DROP SERVER statements.
    • Enables use of the mysqladmin debug command.
    • Enables InnoDB encryption key rotation.
      The corresponding dynamic privilege is ENCRYPTION_KEY_ADMIN.
    • Enables execution of Version Tokens user-defined functions.
      The corresponding dynamic privilege is VERSION_TOKEN_ADMIN.
    • Enables granting and revoking roles, use of the WITH ADMIN OPTION clause of the GRANT statement, and nonempty <graphml> element content in the result from the ROLES_GRAPHML() function.
      The corresponding dynamic privilege is ROLE_ADMIN.
    • Enables control over client connections not permitted to non-SUPER accounts:
      • Enables use of the KILL statement or mysqladmin kill command to kill threads belonging to other accounts. (An account can always kill its own threads.)
      • The server does not execute init_connect system variable content when SUPER clients connect.
      • The server accepts one connection from a SUPER client even if the connection limit configured by the max_connections system variable is reached.
      • A server in offline mode (offline_mode enabled) does not terminate SUPER client connections at the next client request, and accepts new connections from SUPER clients.
      • Updates can be performed even when the read_only system variable is enabled. This applies to explicit table updates, and to use of account-management statements such as GRANT and REVOKE that update tables implicitly.
      The corresponding dynamic privilege for the preceding connection-control operations is CONNECTION_ADMIN.
    You may also need the SUPER privilege to create or alter stored functions if binary logging is enabled, as described in Section 24.7, “Stored Program Binary Logging”.
  • Enables trigger operations. You must have this privilege for a table to create, drop, execute, or display triggers for that table.
    When a trigger is activated (by a user who has privileges to execute INSERT, UPDATE, or DELETE statements for the table associated with the trigger), trigger execution requires that the user who defined the trigger still have the TRIGGER privilege for the table.
  • Enables rows to be updated in tables in a database.
  • This privilege specifier stands for “no privileges.” It is used at the global level with GRANT to specify clauses such as WITH GRANT OPTION without naming specific account privileges in the privilege list. SHOW GRANTS displays USAGE to indicate that an account has no privileges at a privilege level.

Dynamic Privilege Descriptions

Dynamic privileges are defined at runtime, in contrast to static privileges, which are built in to the server. The following list describes each dynamic privilege available in MySQL.
Most dynamic privileges are defined at server startup. Others are defined by a particular server component or plugin, as indicated in the privilege descriptions. In such cases, the privilege is unavailable unless the component or plugin that defines it is enabled.
Particular SQL statements might have more specific privilege requirements than indicated here. If so, the description for the statement in question provides the details.

Privilege-Granting Guidelines

It is a good idea to grant to an account only those privileges that it needs. You should exercise particular caution in granting the FILE and administrative privileges:
  • FILE can be abused to read into a database table any files that the MySQL server can read on the server host. This includes all world-readable files and files in the server's data directory. The table can then be accessed using SELECT to transfer its contents to the client host.
  • GRANT OPTION enables users to give their privileges to other users. Two users that have different privileges and with the GRANT OPTION privilege are able to combine privileges.
  • ALTER may be used to subvert the privilege system by renaming tables.
  • SHUTDOWN can be abused to deny service to other users entirely by terminating the server.
  • PROCESS can be used to view the plain text of currently executing statements, including statements that set or change passwords.
  • SUPER can be used to terminate other sessions or change how the server operates.
  • Privileges granted for the mysql system database itself can be used to change passwords and other access privilege information:
    • Passwords are stored encrypted, so a malicious user cannot simply read them to know the plain text password. However, a user with write access to the mysql.user system table authentication_string column can change an account's password, and then connect to the MySQL server using that account.
    • INSERT or UPDATE granted for the mysql system database enable a user to add privileges or modify existing privileges, respectively.
    • DROP for the mysql system database enables a user to remote privilege tables, or even the database itself.

Static Versus Dynamic Privileges

MySQL supports static and dynamic privileges:
  • Static privileges are built in to the server. They are always available to be granted to user accounts and cannot be unregistered.
  • Dynamic privileges can be registered and unregistered at runtime. This affects their availability: A dynamic privilege that has not been registered cannot be granted.
For example, the SELECT and INSERT privileges are static and always available, whereas a dynamic privilege becomes available only if the server component that implements it has been enabled.
The remainder of this section describes how dynamic privileges work in MySQL. The discussion uses the term “components” but applies equally to plugins.
Note
Server administrators should be aware of which server components define dynamic privileges. For MySQL distributions, documentation of components that define dynamic privileges describes those privileges.
Third-party components may also define dynamic privileges; an administrator should understand those privileges and not install components that might conflict or compromise server operation. For example, one component conflicts with another if both define a privilege with the same name. Component developers can reduce the likelihood of this occurrence by choosing privilege names having a prefix based on the component name.
The server maintains the set of registered dynamic privileges internally in memory. Unregistration occurs at server shutdown.
Normally, a server component that defines dynamic privileges registers them when it is installed, during its initialization sequence. When uninstalled, a server component does not unregister its registered dynamic privileges. (This is current practice, not a requirement. That is, components could, but do not, unregister at any time privileges they register.)
No warning or error occurs for attempts to register an already registered dynamic privilege. Consider the following sequence of statements:
INSTALL COMPONENT 'my_component';
UNINSTALL COMPONENT 'my_component';
INSTALL COMPONENT 'my_component';
The first INSTALL COMPONENT statement registers any privileges defined by server component my_component, but UNINSTALL COMPONENT does not unregister them. For the second INSTALL COMPONENT statement, the component privileges it registers are found to be already registered, but no warnings or errors occur.
Dynamic privileges apply only at the global level. The server stores information about current assignments of dynamic privileges to user accounts in the mysql.global_grants system table:
  • The server automatically registers privileges named in global_grants during server startup (unless the --skip-grant-tables option is given).
  • The GRANT and REVOKE statements modify the contents of global_grants.
  • Dynamic privilege assignments listed in global_grants are persistent. They are not removed at server shutdown.
Example: The following statement grants to user u1 the privileges required to control replication (including Group Replication) on a slave server, and to modify system variables:
GRANT REPLICATION_SLAVE_ADMIN, GROUP_REPLICATION_ADMIN, BINLOG_ADMIN
ON *.* TO 'u1'@'localhost';
Granted dynamic privileges appear in the output from the SHOW GRANTS statement and the INFORMATION_SCHEMA USER_PRIVILEGES table.
For GRANT and REVOKE at the global level, any named privileges not recognized as static are checked against the current set of registered dynamic privileges and granted if found. Otherwise, an error occurs to indicate an unknown privilege identifier.
For GRANT and REVOKE the meaning of ALL [PRIVILEGES] at the global level includes all static global privileges, as well as all currently registered dynamic privileges:
  • GRANT ALL at the global level grants all static global privileges and all currently registered dynamic privileges. A dynamic privilege registered subsequent to execution of the GRANT statement is not granted retroactively to any account.
  • REVOKE ALL at the global level revokes all granted static global privileges and all granted dynamic privileges.
The FLUSH PRIVILEGES statement reads the global_grants table for dynamic privilege assignments and registers any unregistered privileges found there.
For descriptions of the dynamic privileges provided by MySQL Server and server components included in MySQL distributions, see Section 6.2.2, “Privileges Provided by MySQL”.

Migrating Accounts from SUPER to Dynamic Privileges

In MySQL 8.0, many operations that previously required the SUPER privilege are also associated with a dynamic privilege of more limited scope. (For descriptions of these privileges, see Section 6.2.2, “Privileges Provided by MySQL”.) Each such operation can be permitted to an account by granting the associated dynamic privilege rather than SUPER. This change improves security by enabling DBAs to avoid granting SUPER and tailor user privileges more closely to the operations permitted. SUPER is now deprecated and will be removed in a future version of MySQL.
When removal of SUPER occurs, operations that formerly required SUPER will fail unless accounts granted SUPER are migrated to the appropriate dynamic privileges. Use the following instructions to accomplish that goal so that accounts are ready prior to SUPER removal:
  1. Execute this query to identify accounts that are granted SUPER:
    SELECT GRANTEE FROM INFORMATION_SCHEMA.USER_PRIVILEGES
WHERE PRIVILEGE_TYPE = 'SUPER';
  2. For each account identified by the preceding query, determine the operations for which it needs SUPER. Then grant the dynamic privileges corresponding to those operations, and revoke SUPER.
    For example, if 'u1'@'localhost' requires SUPER for binary log purging and system variable modification, these statements make the required changes to the account:
    GRANT BINLOG_ADMIN, SYSTEM_VARIABLES_ADMIN ON *.* TO 'u1'@'localhost';
REVOKE SUPER ON *.* FROM 'u1'@'localhost';
    After you have modified all applicable accounts, the INFORMATION_SCHEMA query in the first step should produce an empty result set.
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