Como usar SQL INYECTION - Inyeccion SQL

A continuación muestro un ejemplo muy sencillo de entender con respecto al funcionamiento de un ataque SQL Inyection.


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# GulfTech Security Research June 20th, 2005
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# Vendor : php Arena
# URL : http://www.phparena.net/pafaq.php
# Version : paFAQ 1.0 Beta 4
# Risk : Multiple Vulnerabilities
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Description:
paFAQ is a FAQ/Knowledge base system that allows webmasters to
keep an organized database of Frequently Asked Questions; a
Knowledge Database for problems and solutions. There are a number
of vulnerabilities in paFaq. These vulnerabilities include
arbitrary unauthorized access to the entire paFaq database, as
well as admin authentication bypass, sql injection, arbitrary
code execution and cross site scripting. An attacker can gain a
remote shell on a vulnerable system using these vulnerabilities.

Cross Site Scripting:
There are some cross site scripting issues in the paFaq software.
Majority of these cross site scripting issues stem from inputted
variables never being sanitized properly.

http:///pafaq/index.php?act=Question&id=1%3E%3Cscript%3Ealert%28
document.cookie%29%3C%2Fscript%3E

These vulnerabilities can be used to render hostile code in the
context of the victims browser, and in turn disclose sensitive
information to an attacker.

SQL Injection:
There are a number of SQL Injection vulnerabilities in paFaq,
but it should be noted that to exploit these issues magic quotes
gpc must be off. Also, magic quotes off seems to be the default
php.ini settings now so I do consider these issues fairly high
risk. The most serious of the SQL Injection issues lies in the
administrative login.

$username = $_REQUEST['username'];
$password = md5($_REQUEST['password']);

$q = $DB->query("SELECT * FROM " . $DB->obj['tbl_pre'] . "admins WHERE
name = '" . $username . "'");
$r = $DB->fetch_row($q);

if ($r['password'] == $password) {

$t = time();
$DB->query("UPDATE " . $DB->obj['tbl_pre'] . "admins SET
session='$t' WHERE id='".$r['id']."'");
setcookie("pafaq_user", $username, time()+3600);
setcookie("pafaq_pass", $password, time()+3600);

The variable $username is taken directly from the submitted login form
and executed in the query, so if magic quotes gpc is off an attacker can
use UNION SELECT to bypass admin authentication!

http://pafaq/admin/index.php?act=login&username='%20UNION%20SELECT%20id,
name,
'3858f62230ac3c915f300c664312c63f',email,notify,permissions,session%20FR
OM%20
pafaq_admins%20WHERE%201/*&password=foobar

The query above uses a UNION SELECT to get the admin username, id, email etc
but we specify the password hash as the md5 encrypted value of the $password
variable. If the host is vulnerable then the above link will log an attacker
in as the first admin in the selected table. Additionally the "id" parameter
in most of the scripts are vulnerable to SQL Injection, and can be
exploited
when magic quotes gpc is set to off.

Arbitrary Database Download:
A very dangerous vulnerability lies in paFaq that will allow for an attacker
to download the entire paFaq database. A user does not have to be logged in
to exploit this vulnerability either, thus making it that more dangerous.

http://path/to/pafaq/admin/backup.php

An attacker can then use the encrypted password hash to gain administrative
access, there is no need for an attacker to decrypt it.

Cookie: pafaq_user=USERNAMEHERE; pafaq_pass=PASSWORDHASH

By adding the above cookie with the required values taken from the
downloaded
database an attacker now has admin access to the affected paFaq
installation.

Arbitrary Code Execution:
Once an attacker has administrative access to the website he can execute any
arbitrary php code by taking advantage of the upload a language pack
feature.
The script does check for a "valid" language pack, but if an attacker, for
example, takes the default en.php file in the language directory and adds a
simple passthru($_GET['cmd']) at the bottom of the page, and then
uploads the
modified en.php after renaming it to something like pafaq.php as a new
language
pack, will be able to execute shell commands on the affected webserver
by calling
the malicious script in the /lang/ directory. Example
/lang/pafaq.php?cmd=id;pwd

Solution:
The developers were contacted and never responded. A quick workaround
would be
to delete the backup.php script, and turn magic quotes gpc on, or better
yet
use a more secure application if deployed live on the web.

Related Info:
The original advisory can be found at the following location
http://www.gulftech.org/?node=research&article_id=00083-06202005

Credits:
James Bercegay of the GulfTech Security Research Team

Obtenido de: http://www.securityfocus.com