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Re: XDomainRequest Integration with AC

From: Maciej Stachowiak <mjs@apple.com>
Date: Fri, 18 Jul 2008 17:07:24 -0700
Cc: Sunava Dutta <sunavad@windows.microsoft.com>, "annevk@opera.com" <annevk@opera.com>, "jonas@sicking.cc" <jonas@sicking.cc>, Sharath Udupa <Sharath.Udupa@microsoft.com>, Zhenbin Xu <Zhenbin.Xu@microsoft.com>, Gideon Cohn <gidco@windows.microsoft.com>, "public-webapps@w3.org" <public-webapps@w3.org>, IE8 Core AJAX SWAT Team <ieajax@microsoft.com>
Message-Id: <228FC43E-6311-4218-BDE7-FD708F3475C4@apple.com>
To: Eric Lawrence <ericlaw@exchange.microsoft.com>

On Jul 18, 2008, at 4:56 PM, Eric Lawrence wrote:

> The specific concern with redirections is that we know of instances  
> where redirection systems are in use that do not currently support  
> addition of custom response headers, and cannot be trivially updated  
> to add such headers.  These redirection systems include legacy C++  
> applications whose source is no longer available; the only possible  
> updates are to the source->destination URLs via a database.  Iíve  
> also heard reports of hardware frontend devices with similar  
> limitations, although Iím not personally aware of a specific device  
> with this limitation.
> In general, checking the Access-control response header on every hop  
> of a redirection chain may make the access-control specification  
> more difficult to deploy in real-world circumstances.

It seems to me that checking every hop is required to avoid  
inadvertent information disclosure. If someone has a service (not  
enabled for Access-Control) which will redirect to the URL of your  
choice but passing some additional info, then by forcing it to  
redirect to a URL that does support Access-Control you can access  
information that you otherwise would not be able to. We should not  
allow systems that don't opt in to be subject to any information  
disclosure, and this seems even more essential if these systems cannot  
be modified.


> -Eric
> From: Sunava Dutta
> Sent: Friday, July 18, 2008 4:21 PM
> To: annevk@opera.com; jonas@sicking.cc; Sharath Udupa; Zhenbin Xu;  
> Gideon Cohn
> Cc: public-webapps@w3.org; IE8 Core AJAX SWAT Team
> Subject: XDomainRequest Integration with AC
> Iím in time pressure to lock down the header names for Beta 2 to  
> integrate XDR with AC. It seems no body has objected to Jonasís  
> proposal. http://lists.w3.org/Archives/Public/public-webapps/2008JulSep/0175.html
> Please let me know if this discussion is closed so we can make the  
> change.
> Namely,
> The changes to support the new Access control model is as follows Ė
> ∑         Change Referer header set in the request to Origin.
> ∑         Change the XDomainRequestAllowed header check from it  
> being ď1Ē to check for Access-Control: allow <*>
> In addition, I realized that the discussions we had in the F2F  
> (tracked by issue 32http://www.w3.org/2008/webapps/track/issues/32)  
> means that an access control check is now also performed when the  
> redirect steps are applied to prevent data leakage from intranet  
> pages. This is different from XDR as we currently do the check in  
> the final destination for redirection. I think the reason why we did  
> this in XDR was to allow cross domain resources to move around  
> easily. That said, Iím not religious about this issue either way.  
> (Adding my team-mates to hear if they have any concerns).  Iíll ask  
> our dev to make the change, but before that I just wanted to confirm  
> the AC spec will be updated with this. Currently I couldnít find  
> this in the updated spec but I could be wrong.
> Thanks,
Received on Saturday, 19 July 2008 00:08:07 UTC

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