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Re: Origin vs Authority; use of HTTPS (draft-nottingham-site-meta-01)

From: Breno de Medeiros <breno@google.com>
Date: Wed, 11 Feb 2009 16:16:10 -0800
Message-ID: <29fb00360902111616o7837b3c1nb1b478a477282a9@mail.gmail.com>
To: Adam Barth <w3c@adambarth.com>
Cc: Eran Hammer-Lahav <eran@hueniverse.com>, "www-talk@w3.org" <www-talk@w3.org>
On Wed, Feb 11, 2009 at 3:57 PM, Adam Barth <w3c@adambarth.com> wrote:

> On Wed, Feb 11, 2009 at 3:32 PM, Breno de Medeiros <breno@google.com>
> wrote:
> > In that case, content-type is a mild defense. Can you give me an example
> > where a web-site administrator will allow files to be hosted at '/'?
>
> There are enough of these sites to force Adobe to break backwards
> compatibility in a Flash security release.
>
> > I can find some fairly interesting names to host at '/'
> >
> > E.g.: favicon.ico, .htaccess, robots.txt, ...
>
> OMG, you changed my favicon!  .htaccess only matters if Apache
> interprets it (e.g., uploading an .htaccess file to Gmail doesn't do
> anything interesting).
>
> > Trying to secure such environments seems to me a waste of time, quite
> > frankly.
>
> Clearly, Adobe doesn't share your opinion.
>
> > The most interesting threat of files uploaded to root is via defacement.
> > This solution does nothing against that threat.
>
> I you can deface my server, then I've got big problems already (e.g.,
> my Web site is totally hacked).  Not addressing this issue creates a
> security problem where none currently exists.


The web site of your corporation being totally hacked and the identity
system for users of your corporation server's being totally hacked are
problems of a completely different order of magnitude.

The fact is that site-meta will be used for purposes that introduce
attending threats even more significant than XSS (an example of which you
still have to provide in this thread) and security measures needed to
mitigate these threats are application specific.



>
>
> >> 1) Require host-meta to be served with a particular, novel Content-Type.
> >
> > Not feasible, because of limitations on developers that implement these
> > server-to-server techniques.
>
> That's an opinion.  We'll see if you're forced to patch the spec when
> you're confronted with a horde of Web servers that you've just made
> vulnerable to attack.
>
> >> 2) Add a section to Security Considerations that explains that
> >> applications using host-meta should consider adding requirement (1).
> >
> > No. I would suggest adding a Security Considerations that say that
> host-meta
> > SHOULD NOT be relied upon for ANY security-sensitive purposes
> _of_its_own_,
>
> Then how are we to address use case (1)?
>
> > and that applications that require levels of integrity against defacement
> > attacks, etc., should implement real security techniques. Frankly, I
> think
> > content-type does very little for security of such applications.
>
> Your argument for why strict Content-Type handling is insecure is that
> a more powerful attacker can win anyway.  My argument is that we have
> implementation experience that we need to defend against these
> threats.
>
> I did a little more digging, and it looks like Silverlight's
> clientaccesspolicy.xml also requires strict Content-Type processing:
>
> http://msdn.microsoft.com/en-us/library/cc645032(VS.95).aspx<http://msdn.microsoft.com/en-us/library/cc645032%28VS.95%29.aspx>
>
> That makes 3 out of 3 systems that use strict Content-Type processing.
>
> Microsoft's solution to the limited hosting environment problem
> appears to be quite clever, actually.  I couldn't find documentation
> (and haven't put in the effort to reverse engineer the behavior), but
> it looks like they require a content type of applciation/xml, which
> they get for free from limiting hosting providers by naming their file
> with a ".xml" extension.  This is clever, because it protects all the
> sites I listed earlier because those sites would have XSS if they let
> an attacker control an application/xml resource on their server.
>
> Adam
>



-- 
--Breno

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Received on Thursday, 12 February 2009 00:16:50 GMT

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