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Re: Websense Enterprise 6.3.3 Policy Bypass
From: "Thor (Hammer of God)" <Thor () hammerofgod com>
Date: Sun, 30 May 2010 20:48:21 +0000

The "no logging at all" bit is the clincher.   I don't see how they could go without fixing it in any "current" version 
of the software.

ISA logging will be turned on by default, but only to the local SQLE instance and only for 7 running days.  That's no 
mitigating factor at all...  People who purchase Websense are counting on the logging as you said.  That's a big "wow" 
for me.  From what I've heard we've got lots of .gov's using websense, and logging and reporting are critical, if not 
legal requirements in many cases. 

Very nice find - and thanks for letting us know.

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: Sunday, May 30, 2010 1:33 PM
To: full-disclosure () lists grok org uk
Subject: Re: [Full-disclosure] Websense Enterprise 6.3.3 Policy Bypass


I wouldn't call breaking proxy chaining mitigation, either.  More like a "quick
fix", if and only if it works.  Or maybe you'd call it a "work-around", which is
what I called it in the first place.

No, there's nothing at all in the Websense database indicating you went to
playboy.com.  You are home free until someone decides to look at the ISA
logs (if logging is turned on) and finds it in there.  But you spent good money
on Websense and want pretty reports with charts and colors and your
company logo, right?

In that way, this is much better than my 2007 User-Agent hack (now fixed).
Your indiscretions were logged, but not blocked or categorized.


Now, as far as stripping out the Via header at ISA goes, per RFC 2616...

"Multiple Via field values represents each proxy or gateway that has
forwarded the message. Each recipient <shout> MUST </shout> append its
information such that the end result is ordered according to the sequence of
forwarding applications."

"MUST append..." does not mean, in my understanding of the English
language (and RFC 2119), "delete the downstream device's Via header".
If you do anything other than "append..." (which you MUST do), you're
breaking the RFC.

And if you go around breaking RFCs, you're BAD, m'kay? ;-)

Link to 2007 User-Agent hack, just in case you missed it...

http://mrhinkydink.blogspot.com/2007/12/websense-policy-filtering-
bypass.html

-------- Original Message --------
Subject: RE: [Full-disclosure] Websense Enterprise 6.3.3 Policy Bypass
From: "Thor (Hammer of God)" <Thor () hammerofgod com>
Date: Sun, May 30, 2010 2:19 pm
To: "dink () mrhinkydink com" <dink () mrhinkydink com>
Cc: "full-disclosure () lists grok org uk"
<full-disclosure () lists grok org uk>

Ah, authenticating at the web proxy *chain*. That wasn't intuitive from the
original post... "breaking" the chain by requiring an auth mechanism that the
downstream proxy doesn't support really isn't a "mitigation,"
but now I understand the basis of the statement.

But, if they fixed it in 7.x, then it obviously wasn't "B" below. ISA wouldn’t
work like that anyway. It doesn't "send requests to the plug-in." You either
use a filter or you don't. For instance, if I simply used the web proxy filter
instead, I could filter for "Via:" and block it. But then again, if I had to do that, I
wouldn't have purchased Websense but rather handled all my blocking at ISA.

Not that it really matters to me personally, but I am curious - is the logging of
the request completely dropped, or is it just not logged as a "filtered
request." IOW, if I'm behind the downstream proxy, and I go to playboy.com,
Web sense logs the request and part of the logging is that it was "filtered" or
"blocked" or something. But if I set "Via" in the downstream proxy (or at the
client via something like firefox) and go to playboy.com, not only do I reach
the site, but there is no record whatsoever that I went to playboy? If it is the
latter, then they would HAVE to fix it in 6.3.3 IMO.

t


-----Original Message-----
From: dink () mrhinkydink com [mailto:dink () mrhinkydink com]
Sent: Sunday, May 30, 2010 10:47 AM
To: Thor (Hammer of God)
Cc: full-disclosure () lists grok org uk
Subject: RE: [Full-disclosure] Websense Enterprise 6.3.3 Policy Bypass


Chaining downstream proxies to ISA and requiring Windows Integrated
Auth has been an issue for a long time (it generally breaks the chain,
so that fixes the bypass problem right there), but frankly I'm guessing.

Windows Auth brings a lot of incompatibilities with it. I wouldn't
recommend it unless it was absolutely required, but its
proxy-chain-breaking properties are legendary.

The ISA server will continue to log, even though Websense won't, so you
do have that. But ISA won't filter, so you're back to square one. And
comparing the two databases for discrepancies can get ugly. By the time
you get around to comparing the databases, the damage has already been
done.
It becomes a forensics exercise at that point.

What I think is going on here is either:

A) The Websense ISA plug-in sees that the request has come in by proxy
and assumes it has already been filtered by the originating proxy

or...

B) ISA sees the request has come in by proxy and therefore doesn't send
the request to the Websense ISA plug-in for filtering.

If it's "B", then it's a Microsoft issue and it may never get fixed
(and it becomes marketing bullet point for ISA Server TMG).

If the same problem occurs in a SQUID integration of Websense 6.3.3,
then it's definitely "A".

I have a feeling Websense fixed it in the 7.x series, so they're
probably not motivated to fix it in 6.x. Again, I don't have the
resources to test that theory (and I asked Dan Hubbard politely for a
temporary license for research purposes).

My hunch is they did fix it in 7.x because they pretty much ignored me
after the first e-mail I sent back in October 2009.

-------- Original Message --------
Subject: RE: [Full-disclosure] Websense Enterprise 6.3.3 Policy Bypass
From: "Thor (Hammer of God)"
Date: Sun, May 30, 2010 12:30 pm
To: "dink () mrhinkydink com" , "full-
disclosure () lists grok org uk"

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
Hosted and sponsored by Secunia - http://secunia.com/

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