After a fresh install of mysql at our linux box server. I was able to login to mysql with any user which we didn't defined.
[root@spica ~]# mysql -utest
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 12
Server version: 5.1.61 Source distribution
Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> quit
Bye
[root@spica ~]# mysql -utest
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 12
Server version: 5.1.61 Source distribution
Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> quit
Bye
To fix you need to delete the blank user at the mysql.user tables.
[root@spica ~]# mysql -uroot -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 14
Server version: 5.1.61 Source distribution
Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| test |
+--------------------+
3 rows in set (0.00 sec)
mysql> select user,host from mysql.user;
+------+------------+
| user | host |
+------+------------+
| root | 127.0.0.1 |
| | localhost |
| root | localhost |
| | meitnerium |
| root | meitnerium |
+------+------------+
5 rows in set (0.00 sec)
mysql> delete from mysql.user where user='';
Query OK, 2 rows affected (0.00 sec)
mysql> select user,host from mysql.user;
+------+------------+
| user | host |
+------+------------+
| root | 127.0.0.1 |
| root | localhost |
| root | meitnerium |
+------+------------+
3 rows in set (0.00 sec)
mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)
mysql> quit
Bye
[root@spica ~]# mysql -utest
ERROR 1045 (28000): Access denied for user 'test'@'localhost' (using password: NO)
[root@spica ~]#
