Re: Websense Enterprise 6.3.3 Policy Bypass

[<dink () mrhinkydink com>]

When you look at the "MUSTs" for Via in RFC 2616, there are only three. 
None of them seem to be applicable here.  And, of course, nowhere does
it say a client MUST NOT fake a Via header. ;-)

So you have an assumption that if an HTTP request with a Via header
passes through your device it must have gotten there legitimately and it
must be treated accordingly.

In other words, this trick may have untapped potential.

-------- Original Message --------
Subject: Re: [Full-disclosure] Websense Enterprise 6.3.3 Policy Bypass
From: Christian Sciberras <uuf6429 () gmail com>
Date: Sun, May 30, 2010 1:40 pm
To: "Thor (Hammer of God)" <Thor () hammerofgod com>
Cc: "dink () mrhinkydink com" <dink () mrhinkydink com>, 
"full-disclosure () lists grok org uk" <full-disclosure () lists grok org uk>

My first thought on this find was "cool".

However the more I think about this, the more I think there's something
seriously amiss.

I would assume that there is some inside code which specifically tells
it to turn off everything when "via" is used?
 If this is so, what stops us from concluding this was some sort of
backdoor?
The only other reason for this would be them trying to support "via" but
did a(n extremely) bad job about it.


Cheers.
 Christian Sciberras




On Sun, May 30, 2010 at 6:30 PM, Thor (Hammer of God)
<Thor () hammerofgod com> wrote:
 Adding "Via:" completely bypasses monitoring too??  That is bad.  I've
never used Websense,  so pardon my ignorance, but this wouldn't apply to
with ISA's native monitoring and logging,  so I'm just curious about
what's going on under the covers.   "Via:" bypassing the filter is "not
good" but bypassing monitoring (and presumably logging) is really bad. 
Nice find.
 
 I am curious as to what your thoughts are regarding Windows Auth as a
mitigation.   While it's nice that ISA could help solve a problem with
Websense, I'm don't see how that would work.  How would requiring auth
solve Websense's inability to filter "Via:" headers?
 
 t
 

> -----Original Message-----
> From: full-disclosure-bounces () lists grok org uk
[mailto:full-disclosure-
> bounces () lists grok org uk] On Behalf Of dink () mrhinkydink com
> Sent: Saturday, May 29, 2010 8:25 PM
> To: full-disclosure () lists grok org uk
> Subject: [Full-disclosure] Websense Enterprise 6.3.3 Policy Bypass
>
> discovered by mrhinkydink
>
> PRODUCT: Websense Enterprise v6.3.3
>
> EXPOSURE: Trivial Web Policy Bypass
>
>
> SYNOPSIS
> ========
>
> By adding a "Via:" header to an HTTP request it is possible for a user
to
> completely bypass filtering and monitoring in a Websense Enterprise
> 6.3.3/Microsoft ISA Server (2004 or 2006) proxy integration
environment.
> PROOF OF CONCEPT
> ================
>
> The following works in a Websense 6.3.3 Enterprise system using the
ISA
> Server integration product and transparent authentication. It is
assumed it will
> work with other proxy integration products, but this has not been
tested.
> I. Install Firefox >= 3.5
>
> II. Obtain and install the Modify Headers plug-in by Gareth Hunt
>
> III. Configure the plug-in to add a valid "Via:" header to every
request
> Example: "Via: 1.1 VIAPROXY"
>
> IV. Browse to a filtered Web site
>
> V. All content is allowed without monitoring
>
>
> PoC VIDEO!
> ==========
>
> http://www.youtube.com/watch?v=H520rQ8JOLY
>
>
> PoC RESTRICTIONS
> ================
>
> The Modify Headers plug-in does not work with SSL. However, in
practice a
> user could browse to a so-called (by Websense) "Proxy Avoidance" Web
site
> and use the SSL capabilities of the remote proxy.
>
>
> OTHER USES
> ==========
>
> Properly configured, a downstream SQUID proxy can send requests to the
> upstream ISA server and all requests will pass through without
blocking or
> monitoring. No evidence of activity will be logged by Websense. This
was in
> fact how this vulnerability was originally discovered.
> Considering the simplicity of the attack, the author suspects this
bypass
> technique is already well-known in certain circles.
>
> Also, it is trivial to modify proxy-enabled Linux utilities to
leverage this bypass.
> The author has recompiled (that is, HACKED) OpenVPN, connect-proxy,
> PuTTY, stunnel, and others to take advantage of this policy bypass.
>
> Obviously, the risk of undetected (by Websense, at least) covert
tunnels is
> high in a vulnerable installation of this product.
>
> Linux platforms using this method in this specific environment will
also enjoy
> bypassing Websense's transparent authentication requirement.
>
>
> WORK-AROUNDS
> ============
>
> For this specific installation scenario (Websense 6.3.3 + ISA 2004/6 +
> transparent authentication), none are known. The following may work:
>
> * Use Windows Integrated Authentication on the ISA Server
>
> * Upgrade to Websense 7.x
>
> * Do not use a proxy integration product
>
>
> HISTORY
> =======
>
> 10/09/2009 - vendor notified
>
> 05/29/2010 - PoC published
>
>
> URL
> ===
>
> http://mrhinkydink.blogspot.com/2010/05/websense-633-via-bypass.html
>
>
> c. MMX mrhinkydink
>
>
> _______________________________________________
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 _______________________________________________
 Full-Disclosure - We believe in it.
 Charter: http://lists.grok.org.uk/full-disclosure-charter.html
 Hosted and sponsored by Secunia - http://secunia.com/

_______________________________________________
Full-Disclosure - We believe in it.
Charter: http://lists.grok.org.uk/full-disclosure-charter.html
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