加強MySQL用戶安全

     很多親們在安裝好了MySQL資料庫之後，對於mysql用戶表並沒有做任何特殊的處理，因此缺省情況下，存在密碼為空的用戶，也有很多用戶名和密碼都為空的情形，我們稱為雙空用戶。這種情形下的登錄，在此統稱為異常登陸。對於生產環境的資料庫來說，這會帶來一些不確定的安全隱患。以下是關於這個問題的描述以及清理掉無關用戶的方法。
    相關mysql用戶相關參考：
MySQL 用戶與權限管理
MySQL 修改用戶密碼及重設root密碼

1、演示異常登入

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        |
+---------------------------------------------------------------------+

3、小結

a、對於部署到生產環境的mysql伺服器建議清理所有密碼為空的用戶以及雙空用戶b、建議清理前先備份，使用drop user方式來清理用戶更穩

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