Message-ID: <optid.4766fb6a09.58DB1B68E62B9F448DF1A276B0886DF11C6CF102@EX2010.hammerofgod.com>
Date: Sun, 30 May 2010 18:19:40 +0000
From: "Thor (Hammer of God)" <Thor@...merofgod.com>
To: "dink@...inkydink.com" <dink@...inkydink.com>
Cc: "full-disclosure@...ts.grok.org.uk" <full-disclosure@...ts.grok.org.uk>
Subject: Re: Websense Enterprise 6.3.3 Policy Bypass

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@...inkydink.com [mailto:dink@...inkydink.com]
>Sent: Sunday, May 30, 2010 10:47 AM
>To: Thor (Hammer of God)
>Cc: full-disclosure@...ts.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)" <Thor@...merofgod.com>
>Date: Sun, May 30, 2010 12:30 pm
>To: "dink@...inkydink.com" <dink@...inkydink.com>, "full-
>disclosure@...ts.grok.org.uk" <full-disclosure@...ts.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@...ts.grok.org.uk
>>[mailto:full-disclosure- bounces@...ts.grok.org.uk] On Behalf Of
>>dink@...inkydink.com
>>Sent: Saturday, May 29, 2010 8:25 PM
>>To: full-disclosure@...ts.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
>>
>>
>>_______________________________________________
>>Full-Disclosure - We believe in it.
>>Charter: http://lists.grok.org.uk/full-disclosure-charter.html
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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/

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