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Re: XHR without user credentials

From: Adam Barth <w3c@adambarth.com>
Date: Sat, 13 Jun 2009 14:45:32 -0700
Message-ID: <7789133a0906131445s4dd80272ha7ae966515a8980e@mail.gmail.com>
To: Tyler Close <tyler.close@gmail.com>
Cc: "Mark S. Miller" <erights@google.com>, Anne van Kesteren <annevk@opera.com>, public-webapps <public-webapps@w3.org>
On Sat, Jun 13, 2009 at 12:20 PM, Tyler Close<tyler.close@gmail.com> wrote:
> On Sat, Jun 13, 2009 at 10:23 AM, Adam Barth<w3c@adambarth.com> wrote:
>> For example, GuestXHR could be used to mount a login CSRF attack.
> Are you sure about that? Since the response won't carry the
> Access-Control-Allow-Origin header, the browser shouldn't set any
> cookies. I don't see how this attack works.

Why do you assume the response won't carry the header
"Access-Control-Allow-Origin: *" ?  That just means the content of the
response is public, which might well be true.

>> Alternatively, if the server is using IP-based authenication, it could
>> be used to mount a CSRF attack (e.g., inflate the bill at the ACM
>> digital library, which uses IP-based authentication).
> Since such servers aren't currently looking for the Origin header,
> adding the header still won't protect them.

Which is why we're discussing servers that act use the Origin header
as a CSRF defense, as described in draft-abarth-origin.

> I'm also not sure they would block on the header if they did know about it.

That's what the spec tells them to do.

> If they think
> IP-based authentication is good enough, are they really going to
> reject a request with "Origin: null"?

IP-based authentication works great for the ACM digital library.  I
don't know of any other authentication technology that better suits
their use case.  I wouldn't assume they're clueless about security.

In any case, this whole discussion is a bit silly.  You haven't
advanced any reason not to send Origin: null.  We can continue this
discussion at a later time when GuestXHR is further along the
standardization process.

Received on Saturday, 13 June 2009 21:46:29 UTC

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