I. description
 It is found that MySQL has a low-risk vulnerability. You can write your own scheme, test yourself, and upgrade yourself.
Version: upgrade MySQL 5.7.25 to the latest version of MySQL 5.7.28.
Architecture: master-slave architecture

II. Upgrading process
 1. Download the latest database software MySQL 5.7.28
 2. Upload to the specified directory
 3. Backup database software, database data directory, my.cnf
 4. Decompress the database software to the specified path
 5. Close the standby Library
 6. Use the new software to start the standby database, mysqld_safe&
7. Log in to the standby database and find that the version has been upgraded. Use MySQL? Upgrade command to upgrade the system database
 8. If no error is reported, restart the standby database.
9. The main warehouse goes through the standby warehouse process
 10. Finally, confirm whether the active and standby databases are consistent

III. some contents
# mysql_upgrade -uroot -p
mysql_upgrade: [Warning] Using a password on the command line interface can be insecure.
Checking if update is needed.
Checking server version.
Running queries to upgrade MySQL server.
Checking system database.
mysql.columns_priv                                 OK
mysql.db                                           OK
mysql.engine_cost                                  OK
mysql.event                                        OK
mysql.func                                         OK
mysql.general_log                                  OK
mysql.gtid_executed                                OK
mysql.help_category                                OK
mysql.help_keyword                                 OK
mysql.help_relation                                OK
mysql.help_topic                                   OK
mysql.innodb_index_stats                           OK
mysql.innodb_table_stats                           OK
mysql.ndb_binlog_index                             OK
mysql.plugin                                       OK
mysql.proc                                         OK
mysql.procs_priv                                   OK
mysql.proxies_priv                                 OK
mysql.server_cost                                  OK
mysql.servers                                      OK
mysql.slave_master_info                            OK
mysql.slave_relay_log_info                         OK
mysql.slave_worker_info                            OK
mysql.slow_log                                     OK
mysql.tables_priv                                  OK
mysql.time_zone                                    OK
mysql.time_zone_leap_second                        OK
mysql.time_zone_name                               OK
mysql.time_zone_transition                         OK
mysql.time_zone_transition_type                    OK
mysql.user                                         OK
Found outdated sys schema version 1.5.1.
Upgrading the sys schema.
Checking databases.
sys.sys_config                                     OK
Upgrade process completed successfully.
Checking if update is needed.

mysql> status
--------------
mysql  Ver 14.14 Distrib 5.7.28, for linux-glibc2.12 (x86_64) using  EditLine wrapper

Connection id:      2
Current database:   
Current user:       root@localhost
SSL:            Not in use
Current pager:      stdout
Using outfile:      ''
Using delimiter:    ;
Server version:     5.7.28-log MySQL Community Server (GPL)
Protocol version:   10
Connection:     Localhost via UNIX socket
Server characterset:    utf8mb4
Db     characterset:    utf8mb4
Client characterset:    utf8mb4
Conn.  characterset:    utf8mb4
UNIX socket:        /tmp/mysql.sock
Uptime:         27 sec