Papoo CMS: Authenticated Arbitrary Code Execution
The Papoo CMS allows authenticated users to upload GIF, JPG and PNG images if they have the "upload images" privilege, which is true for all default groups that can access the administrative interface. The CMS checks the uploaded images only for their header, but not for the file extension. It is therefore possible to upload images with the file extension ".php" and a valid image header. By embedding PHP code into the image (e.g. by using the GIF comments field), arbitrary code can be executed when requesting the image.
Product: Papoo CMS
Affected Versions: 3.7.3 (older versions are probably also vulnerable)
Fixed Versions: 3.7.3 after applying vendor patch
Vulnerability Type: Code Execution
Security Risk: medium
Vendor URL: http://www.papoo-cms.com
Vendor Status: notified, fixed version released
Advisory URL: http://www.redteam-pentesting.de/advisories/rt-sa-2009-005
Advisory Status: published
CVE URL: TBA
"Papoo CMS is one of the best accessible CMS systems available on the market. Furthermore, it can be handled easily in the backend as well as designed very individually in the frontend. Besides being accessible, our main characteristics are the high individuality regarding the layout and ease of operation. Go and convince yourself on our reference page. With Papoo you can create your web page easier, better, more optimized for search engines and accessible. See here the most important advantages of CMS Papoo at a glance."
(from the vendor's homepage)
The Papoo CMS implements a role based authentication model which allows to give groups the right to upload GIF, JPG or PNG images to the CMS. The default groups "Administratoren" (administrators), "Redakteure" (editors) and "Chefredakteure" (chief editors) all have have this right enabled. It is not allowed to upload PHP files via the "Dateien verwalten -> Dateien hochladen" (manage files -> upload files) submenu, as the extension ".php" is forbidden.
The "Bilder verwalten -> Bilder hochladen" (manage images -> upload images) submenu does not check the images to be uploaded for their extension, but only for a valid image header. It is therefore possible to create an image with a valid header and the extension ".php" and upload it to the CMS. Inside the image, arbitrary PHP code can be embedded. When the image is requested by e.g. the browser, the web server will execute the PHP code inside due to the image's ".php" file extension.
Proof of Concept
The following command will generate a file with a valid GIF header which runs the phpinfo() function when requested:
$ printf "GIF89a\x01\x00\x01\x00<?php phpinfo();?>" > poc.php
Upload the file with the "Bilder verwalten -> Bilder hochladen" submenu. It is not necessary to complete the second upload dialog where you can enter additional information about the image, as it will already be available at the URL
A possible workaround is to disable the PHP Engine for the directory that images are uploaded to. Note that there is a valid PHP script _spamcode_image.php within that directory which might be required by the CMS to operate correctly.
The vendor released a patched version of 'image_core_class.php' that must replace the file 'lib/classes/image_core_class.php' in existing Papoo installations .
NOTE: The archive containing the current version 3.7.3 of Papoo does
NOT contain a fix. Users downloading the latest version of Papoo MUST apply the fix after installation.
It is common for Content Management Systems like Papoo to have users with restricted access to the application, e.g. editors who can edit or create pages on a certain level. Those users normally do not have any system rights on the web server. This vulnerability enables them to execute arbitrary PHP code with the runtime permissions of the web server hosting the CMS. It is deemed a medium risk, as the user has to be authenticated to the CMS and has to have the "upload images" privilege.
2009-05-15 Vulnerability identified during a penetration test
2009-05-20 Client notified
2009-06-05 CVE number requested
2009-06-05 Vendor notified
2009-06-30 Vendor releases patch
2009-08-10 Advisory released
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