Advisory: Remote Code Execution in TYPO3 Extension ke_dompdf

During a penetration test RedTeam Pentesting discovered a remote code
execution vulnerability in the TYPO3 extension ke_dompdf, which allows
attackers to execute arbitrary PHP commands in the context of the
webserver. 


Details
=======

Product: ke_dompdf TYPO3 extension
Affected Versions: 0.0.3<=
Fixed Versions: 0.0.5
Vulnerability Type: Remote Code Execution
Security Risk: high
Vendor URL: http://typo3.org/extensions/repository/view/ke_dompdf
Vendor Status: fixed version released
Advisory URL: https://www.redteam-pentesting.de/advisories/rt-sa-2014-007
Advisory Status: published
CVE: CVE-2014-6235
CVE URL: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2014-6235


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

"DomPDF library and a small pi1 to show how to use DomPDF to render the
current typo3-page to pdf."
(taken from the extension's description)


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

The TYPO3 extension ke_dompdf contains a version of the dompdf library
including all files originally supplied with it. This includes an
examples page, which contains different examples for HTML-entities
rendered as a PDF.  This page also allows users to enter their own HTML
code into a text box to be rendered by the webserver using dompdf.
dompdf also supports rendering of PHP files and the examples page also
accepts PHP code tags, which are then executed and rendered into a PDF
on the server.

Since those files are not protected in the TYPO3 extension directory,
anyone can access this URL and execute arbitrary PHP code on the system.
This behaviour was already fixed in the dompdf library, but the typo3
extension ke_dompdf supplies an old version of the library that still
allows the execution of arbitrary PHP code.


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

Access examples.php on the vulnerable system:
http://www.example.com/typo3conf/ext/ke_dompdf/res/dompdf/www/examples.php

Enter PHP code in the text box on the bottom of the page and click the
submit button, for example:

------------------------------------------------------------------------
<?php phpinfo() ?>
------------------------------------------------------------------------

The page will return a PDF file containing the output of the PHP code.


Workaround
==========

Remove the directory "www" containing the examples.php file or at least
the examples.php file from the extensions' directory.


Fix
===

Update to version 0.0.5 of the extension.


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

high


Timeline
========

2014-04-21 Vulnerability identified
2014-04-30 Customer approved disclosure to vendor
2014-05-06 CVE number requested
2014-05-10 CVE number assigned
2014-05-13 Vendor notified
2014-05-20 Vendor works with TYPO3 security team on a fix
2014-09-02 Vendor released fixed version [2]
2014-12-01 Advisory released


References
==========

The TYPO3 extension ke_dompdf contains an old version of the dompdf
library, which contains an example file that can be used to execute
arbitrary commands.  This vulnerability was fixed in dompdf in 2010. The
relevant change can be found in the github repository of dompdf:

[1] https://github.com/dompdf/dompdf/commit/
    e75929ac6393653a56e84dffc9eac1ce3fb90216

TYPO3-EXT-SA-2014-010: Several vulnerabilities in third party extensions:

[2] http://typo3.org/teams/security/security-bulletins/typo3-extensions/
    typo3-ext-sa-2014-010/


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

RedTeam Pentesting offers individual penetration tests, short pentests,
performed by a team of specialised IT-security experts. Hereby, security
weaknesses in company networks or products are uncovered and can be
fixed immediately.

As there are only few experts in this field, RedTeam Pentesting wants to
share its knowledge and enhance the public knowledge with research in
security-related areas. The results are made available as public
security advisories.

More information about RedTeam Pentesting can be found at
https://www.redteam-pentesting.de.

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