Advisory 02/2005: Remote code execution in Serendipity

From: Christopher Kunz (christopher.kunz_at_hardened-php.net)
Date: 06/30/05

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                             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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