Joomla Weak Random Password Reset Token Vulnerability

Advisory Content :

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SektionEins GmbH
www.sektioneins.de

-= Security Advisory =-

Advisory: Joomla Weak Random Password Reset Token Vulnerability
Release Date: 2008/09/11
Last Modified: 2008/09/11
Author: Stefan Esser [stefan.esser[at]sektioneins.de]

Application: Joomla <= 1.5.7
Severity: Usage of mt_rand() and mt_srand() for generation
of cryptographic secrets like random password
reset tokens
Risk: High
Vendor Status: Vendor has released a partially fixed Joomla 1.5.7
Reference: http://www.sektioneins.de/advisories/SE-2008-04.txt

http://www.suspekt.org/2008/08/17/mt_srand-and-not-so-random-numbers/

Overview:

Quote from http://www.joomla.org
"Joomla is an award-winning content management system (CMS), which
enables you to build Web sites and powerful online applications.
Many aspects, including its ease-of-use and extensibility, have
made Joomla the most popular Web site software available."

During an analysis of the password reset vulnerability fixed in
Joomla 1.5.6 we realized that Joomla does not only generate random
password reset tokens with mt_rand(), which is not secure enough
for cryptographic secrets anyway, but additionally initializes the
PRNG with a weak seed that results in less than 1.000.000 possible
password reset tokens.

Because there are only 1.000.000 possible password reset tokens an
attacker can trigger a reset of the admin password and then try out
all possible password reset tokens until he finds the correct one.
Even with a home DSL line (as used in germany) breaking into the
admin account should be possible in less than 3 hours. However
attackers are usually bouncing over much faster hosts.

In response to our report Joomla 1.5.7 was released (without sharing
the patch with us prior the release) which replaces the very weak PRNG
seeding with a new seed that is about 2^32 in strength. While this
stops the simple brute forcing attack Joomla's password reset token
is still vulnerable to mt_rand() leak attacks and because Joomla still
seeds the PRNG with mt_srand() it is a potential threat to other PHP
applications or plugins using mt_rand() on the same server.

Details:

The problems arising from using mt_(s)rand for cryptographic secrets
and possible attacks against PHP's PRNG and PHP applications using it
are explained by the blog post "mt_(s)rand and not so random numbers"
which is available here:

http://www.suspekt.org/2008/08/17/mt_srand-and-not-so-random-numbers/

Proof of Concept:

SektionEins GmbH is not going to release a proof of concept
exploit for this vulnerability.

Disclosure Timeline:

15. Aug 2008 - Sent notification to Joomla about the vulnerability
20. Aug 2008 - Resent notification because no reply from Joomla
20. Aug 2008 - Received confirmation
21. Aug 2008 - Received a forwarded message from vendor-sec discussing
the vulnerability - obviously Joomla shared our report
with vendor-sec without asking or notifying us.
21. Aug 2008 - In a reply to the forwarded message we recommended NOT
TO USE mt_srand for the password reset
03. Sep 2008 - On Joomla.org appears a blog post notifying their users
that they should upgrade to Joomla 1.5.6 immediately
because of security issues with the password reset
09. Sep 2008 - The Joomla Development Team releases Joomla 1.5.7
without telling us about this or consulting us to review
their patch
11. Sep 2008 - Public Disclosure after learning about the new
Joomla 1.5.7 in the media

Recommendation:

It is recommended to upgrade not only to the latest version of Joomla
which also fixes additional vulnerabilities reported by third parties,
but also to install the Suhosin PHP extension, which comes with a
generic protection against mt_(s)rnad vulnerabilities.

Upgrading only Joomla does not fix the whole problem.

Grab your copies at:

http://www.joomla.org
http://www.suhosin.org

CVE Information:

The Common Vulnerabilities and Exposures project (cve.mitre.org) has
not assigned a name to this vulnerability yet.

GPG-Key:

pub 1024D/15ABDA78 2004-10-17 Stefan Esser <stefan.esser (at) sektioneins
(dot) de [email concealed]>
Key fingerprint = 7806 58C8 CFA8 CE4A 1C2C 57DD 4AE1 795E 15AB DA78

Copyright 2008 SektionEins GmbH. All rights reserved.
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Joomla Weak Random Password Reset Token Vulnerability