Joomla Weak Random Password Reset Token Vulnerability

Credit: Stefan Esser
Risk: High
Local: No
Remote: Yes
CWE: CWE-189

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 SektionEins GmbH -= 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]] 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: Overview: Quote from "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: 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 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: CVE Information: The Common Vulnerabilities and Exposures project ( has not assigned a name to this vulnerability yet. GPG-Key: pub 1024D/15ABDA78 2004-10-17 Stefan Esser <stefan.esser_at_sektioneins&#46;de> Key fingerprint = 7806 58C8 CFA8 CE4A 1C2C 57DD 4AE1 795E 15AB DA78 Copyright 2008 SektionEins GmbH. All rights reserved. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.8 (Darwin) iEYEARECAAYFAkjJLHkACgkQSuF5XhWr2njUYQCgq+5P1O+7llh32KXcCHqdQ/C4 QWoAoJGF6jt3rDyNM3ESDlfUA/NxW3f9 =AA3y -----END PGP SIGNATURE-----


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