[whatwg] AppCache feature request: An https manifest should be able to list resources from other https origins.

Jonas Sicking jonas at sicking.cc
Mon Feb 7 16:35:55 PST 2011

On Mon, Feb 7, 2011 at 3:31 PM, Ian Hickson <ian at hixie.ch> wrote:
> On Mon, 7 Feb 2011, Jonas Sicking wrote:
>> On Mon, Jan 31, 2011 at 6:27 PM, Michael Nordman <michaeln at google.com> wrote:
>> > But... the risk you outline is not possible...
>> >
>> >> However, with the modification you are proposing, an attacker site
>> >> could forever pin this page the users app-cache. This means that if
>> >> there is a security bug in the page, the attacker site could exploit
>> >> that security problem forever since any javascript in the page will
>> >> continue to run in the security context of bunnies.com. So all of a
>> >> sudden the CORS headers that the site added has now had a severe
>> >> security impact.
>> >
>> > The bunnies.com page stored in the attacker's appcache will never be
>> > loaded into the context of bunnies.com. There are provisions in the
>> > the appcache system to prevent that. Those provisions guard against a
>> > this type of attack via HTTP.
>> Your proposal means that we forever lock that constraint on the
>> appcache. That is not currently the case. I.e. we'll never be able to
>> say "open an iframe using the resource which is available in my
>> appcache" or "open this cross-site worker using the resource available
>> in my appcache".
>> Or at least we won't ever be able to do that for cross-site resources.
> That's intentional. We don't want it to be possible to get a cache of a
> third-party page vulnerable to some sort of XSS attack and then to be able
> to load that page with the credentials of its origin, since it would make
> it possible for hostile sites to lock in a vulnerability and keep using
> it even after the site had fixed the problem.

It seems desirable that the third party site could opt in to allowing
this. Especially if it can choose which sites should be able to cache
it. Which I think is the feature request that Michael starts with in
this thread.

/ Jonas

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