Advisory 02/2005: Remote code execution in Serendipity

[Christopher Kunz <christopher.kunz () hardened-php net>]

                        Hardened PHP Project
                        www.hardened-php.net


                      -= Security  Advisory =-


     Advisory: Remote code execution in Serendipity
 Release Date: 2005/06/29
Last Modified: 2005/06/29
       Author: Christopher Kunz <christopher.kunz () hardened-php net>
  Application: Serendipity <= 0.8.2
     Severity: Arbitrary remote code execution
         Risk: Very High
Vendor Status: Vendor has released an updated version
   References: http://www.hardened-php.net/advisory-022005.php


Overview:

   Quote from http://www.s9y.org/:
   "Serendipity is a weblog/blog system, implemented with PHP. It is standards
   compliant, feature rich and open source (BSD License). Serendipity is
   constantly under active development, with a team of talented developers
   trying to make the best PHP powered blog on the net."


Details:

   GulfTech Security [1] recently discovered a vulnerability in the PHP XML RPC
   project [2] that leads to remote code execution. Unfortunately, this vulner-
   ability also exists in the PEAR XMLRPC implementation, and GulfTech somewhat
   neglected to notify the vendors in question.
   Similar to the recently-discovered holes in PostNuke and Drupal, the
   XML-RPC parser in Serendipity allows for remote code execution. An attacker
   can send a forged POST request to the victim's blog and include PHP code in
   the request body. This code is executed in the context of the affected
   Serendipity instance.
   Since the vulnerability is extremely easy to exploit and apart from one POST
   request, no suspicious activity is logged, it could be used for automated
   mass defacements and viral reproduction, similar to Santy.
   The Hardened PHP project had knowledge of that kind of vulnerability for
   some time now but tried to establish a responsible way of coordinating the
   disclosure with all affected parties.
   The maintainer of PEAR::XML_RPC has released an updated version that fixes
   the vulnerability. The Serendipity team has released a fixed version, too.


CVE Information:

   The Common Vulnerabilities and Exposures project (cve.mitre.org) has
   assigned the name CAN-2005-1921 to the vulnerability in PEAR::XML_RPC.


Proof of Concept:

   The Hardened PHP Project is not going to release an exploit for
   this vulnerability to the public.
   It is trivial to implement, anyway.


Disclosure Timeline:

   29. June 2005 - Vulnerability discovered and vendor notified
   29. June 2005 - Vendor released bugfixed version
   29. June 2005 - Public disclosure


Recommendation:

   We urge you to update to the newest version of Serendipity, 0.8.2.
   http://prdownloads.sourceforge.net/php-blog/serendipity-0.8.2.tar.gz
   If, for some reason, that seems unfeasible, you should render the
   file serendipity_xmlrpc.php unreadable by the web server to close the
   most obvious attack vector.


References:

   [ 1 ] http://www.gulftech.org/
   [ 2 ] http://phpxmlrpc.sourceforge.net/


Copyright 2005 Christopher Kunz from the hardened PHP Project. All rights reserved.

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