Advisory 07/2006: phpMyAdmin Multiple CSRF Vulnerabilities



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Hardened-PHP Project
www.hardened-php.net

-= Security Advisory =-


Advisory: phpMyAdmin Multiple CSRF Vulnerabilities
Release Date: 2006/10/01
Last Modified: 2006/10/01
Author: Stefan Esser [sesser@hardened-php.net]

Application: phpMyAdmin <= 2.9.0
Severity: Multiple vulnerabilities within phpMyAdmin allow
bypassing it's protection against CSRF
Risk: Medium Critical
Vendor Status: Vendor has a released an updated version
References: http://www.hardened-php.net/advisory_072006.130.html


Overview:

Quote from http://www.phpmyadmin.net
"phpMyAdmin is a tool written in PHP intended to handle the
administration of MySQL over the Web. Currently it can create and
drop databases, create/drop/alter tables, delete/edit/add fields,
execute any SQL statement, manage keys on fields, manage privileges,
export data into various formats and is available in 50 languages."

During an audit of phpMyAdmin's protection against CSRF: Cross Site
Request Forgeries we discovered that there were multiple ways to
bypass the protection.

The failure of phpMyAdmin's CSRF protection obviously means that a
potential attacker can use CSRF attacks to trick the browser of a
phpMyAdmin user to execute any kind of SQL queries on the victims
database server.


Details:

phpMyAdmin uses a random token that is stored within the user's
session to protect against Cross Site Request Forgeries. CSRF
basically means that a website tricks the browser of a visiting
user into issuing HTTP requests against another site that does
ensure, that the request was intended.

In case of phpMyAdmin a CSRF vulnerability obviously means that
another site could trick the browser of a phpMyAdmin user into
issuing arbitrary SQL queries against his database.

In phpMyAdmin the CSRF protection works like this

1) Start PHP's Session Handling
2) Is there already a token assigned to the session?
-> No: create a random token
3) Is supplied token equal to session token?
-> No: unset() all request variables not in white-list

While this design could actually work the implementation in
phpMyAdmin was vulnerable to multiple attacks because before
and during the 3 steps mentioned several modifications to the
request variable arrays are made and these variables get
globalised. (This is done within the PHP code and has nothing
to do with register_globals)

The attacks we found attack different phases of the CSRF
protection. The following is an overview of the vulnerabilities
within the 3 phases. For each phase several different attacks
are possible. Several of the attacks require GPC variables
with names that are equal to PHP's superglobals, therefore
these attacks are automatically stopped by our Suhosin extension.

[-- Token Verification --]

The token verification could be tricked because there existed
several flaws in the globalisation routine that allowed
destroying the content of the session variables. Additionally
the special handling of session variables during while
register_globals is activated allowed directly setting the
session token from within the URL.
Obviously it is very easy to "guess" the required token when
the token is empty or is set to a value of his choice.

[-- Determine which variables to unset --]

The _REQUEST array was used to determine which variables should
be unset() but phpMyAdmin contained intended and unintended ways
that allowed overwriting the content of the _REQUEST array.
In the new version all GPC arrays are used for this process and
the unintended way to destroy superglobal arrays within the
globalisation was closed.

[-- Unset variables --]

Unset() is a dangerous function because older PHP versions
(that are still installed on most servers) contained
vulnerabilities that allowed bypassing it.

For further information take a look at:

http://www.hardened-php.net/critical_php_vulnerability_explained.124.html


Proof of Concept:

The Hardened-PHP Project is not going to release exploits for
this vulnerability to the public.


Disclosure Timeline:

23. September 2006 - Contacted phpMyAdmin developers by email
01. October 2006 - Updated phpMyAdmin was released
01. October 2006 - Public Disclosure


Recommendation:

It is strongly recommended to upgrade to the newest version of
phpMyAdmin 2.9.0.1 which you can download at:

http://www.phpmyadmin.net/home_page/downloads.php

As usual we very strongly recommend to install our Suhosin PHP
extension. It disallows request variables with the same name
as PHP superglobal arrays. This stops several of the attacks
described in this advisory.

Grab your copy and more information at:

http://www.hardened-php.net/suhosin/index.html


GPG-Key:

http://www.hardened-php.net/hardened-php-signature-key.asc

pub 1024D/0A864AA1 2004-04-17 Hardened-PHP Signature Key
Key fingerprint = 066F A6D0 E57E 9936 9082 7E52 4439 14CC 0A86 4AA1


Copyright 2006 Stefan Esser. All rights reserved.

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