加强MySQL用户安全

a、演示双空用户登陆
[root@xlkoracel ~]# mysql -uroot -p
Enter password: 
(root@localhost) [(none)]> show variables like 'version';
+---------------+--------+
| Variable_name | Value  |
+---------------+--------+
| version       | 5.6.26 |
+---------------+--------+

(root@localhost) [(none)]> select user,host,password from mysql.user;
+-------+-------------+-------------------------------------------+
| user  | host        | password                                  |
+-------+-------------+-------------------------------------------+
| root  | localhost   | *E74858DB86EBA20BC33D0AECAE8A8108C56B17FA |
| root  | xlkoracel   |                                           |
| root  | 127.0.0.1   |                                           |
| root  | ::1         |                                           |
|       | localhost   |                                           |
|       | xlkoracel   |                                           |
| mycat | localhost   | *975B2CD4FF9AE554FE8AD33168FBFC326D2021DD |
| mycat | 192.168.1.% | *975B2CD4FF9AE554FE8AD33168FBFC326D2021DD |
| mycat | 192.168.%.% | *975B2CD4FF9AE554FE8AD33168FBFC326D2021DD |
| root  | 192.168.%.% | *E74858DB86EBA20BC33D0AECAE8A8108C56B17FA |
+-------+-------------+-------------------------------------------+

(root@localhost) [(none)]> -- 可以看到存在用户名和密码同时为空的情形
(root@localhost) [(none)]> -- 退出后尝试使用任意用户名登录
(root@localhost) [(none)]> exit
Bye
[root@xlkoracel ~]# mysql -uxx ###无需指定密码参数-p
(xx@localhost) [(none)]> -- 可以成功登陆
(xx@localhost) [(none)]> -- 下面查看一下自身的权限
(xx@localhost) [(none)]> show grants;  --当前只有usage权限
+--------------------------------------+
| Grants for @localhost                |
+--------------------------------------+
| GRANT USAGE ON *.* TO ''@'localhost' |
+--------------------------------------+

(xx@localhost) [(none)]> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| test               |
+--------------------+

(xx@localhost) [(none)]> use test;
Database changed
(xx@localhost) [test]> show tables;
Empty set (0.00 sec)

(xx@localhost) [test]> create table t(id int);
Query OK, 0 rows affected (0.14 sec)

(xx@localhost) [test]> insert into t values(1);
Query OK, 1 row affected (0.01 sec)

(xx@localhost) [test]> select * from t;
+------+
| id   |
+------+
|    1 |
+------+
1 row in set (0.00 sec)

(xx@localhost) [test]> --从上可以看出，usage权限已经可以完成很多任务
(xx@localhost) [test]> use infromation_schema;
ERROR 1044 (42000): Access denied for user ''@'localhost' to database 'infromation_schema'
(xx@localhost) [test]> exit;


b、演示密码为空的用户登陆
[root@xlkoracel ~]# mysql -uroot -hxlkoracel  ###注，此时也无需指定参数-p  
(root@xlkoracel) [(none)]> --可以成功登陆
(root@xlkoracel) [(none)]> show grants;   --查看自身权限，为ALL PRIVILEGES，权限更大
+---------------------------------------------------------------------+
| Grants for root@xlkoracel                                           |
+---------------------------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'root'@'xlkoracel' WITH GRANT OPTION |
| GRANT PROXY ON ''@'' TO 'root'@'xlkoracel' WITH GRANT OPTION        |
+---------------------------------------------------------------------+

[root@xlkoracel ~]# mysql -uroot -p
Enter password: 
(root@localhost) [(none)]> select user,host,password from mysql.user
    -> where (user is null or user='') and (password is null or password='');
+------+-----------+----------+
| user | host      | password |
+------+-----------+----------+
|      | localhost |          |
|      | xlkoracel |          |
+------+-----------+----------+
2 rows in set (0.01 sec)

(root@xlkoracel) [(none)]> -- Author : Leshami
(root@xlkoracel) [(none)]> -- Blog   : http://blog.csdn.net/leshami
(root@localhost) [(none)]> -- 使用drop 方式清理用户
(root@localhost) [(none)]> drop user ''@'localhost';
Query OK, 0 rows affected (0.24 sec)

(root@localhost) [(none)]> select user,host,password from mysql.user
    -> where (user is null or user='') and (password is null or password='');
+------+-----------+----------+
| user | host      | password |
+------+-----------+----------+
|      | xlkoracel |          |
+------+-----------+----------+
1 row in set (0.00 sec)

(root@localhost) [(none)]> -- 直接用delete从mysql.user表清理用户
(root@localhost) [(none)]> delete from mysql.user
    -> where (user is null or user='') and (password is null or password='');
Query OK, 1 row affected (0.06 sec)

(root@localhost) [(none)]> -- 直接用delete从mysql.user表清理所有密码为空的用户
(root@xlkoracel) [(none)]> delete from mysql.user where password is null or password='';
Query OK, 3 rows affected (0.00 sec)