很多亲们在安装好了mysql数据库之后，对于mysql用户表并没有做任何特殊的处理，因此缺省情况下，存在密码为空的用户，也有很多用户名和密码都为空的情形，我们称之为双空用户。这种情形下的登录，在此统称为异常登陆。对于生产环境的数据库来说，这会带来一些不确定的安全隐患。下面是关于这个问题的描述以及清理掉无关用户的方法。
有关mysql用户相关参考：
mysql 用户与权限管理
mysql 修改用户密码及重置root密码
1、演示异常登录
a、演示双空用户登陆[root@xlkoracel ~]# mysql -uroot -pEnter 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)]> exitBye[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 |+---------------------------------------------------------------------+
2、清理异常用户
[root@xlkoracel ~]# mysql -uroot -pEnter 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://www.php.cn/(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)
3、小结
a、对于部署到生产环境的mysql服务器建议清理所有密码为空的用户以及双空用户
b、建议清理前先备份，使用drop user方式来清理用户更稳妥
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