Re: Subresource Integrity and fingerprinting

Relying on CORS assumes that any sensitive data that should be available
cross-origin would have appropriate headers applied to any response.

-mike

--
Mike West <mkwst@google.com>
Google+: https://mkw.st/+, Twitter: @mikewest, Cell: +49 162 10 255 91

Google Germany GmbH, Dienerstrasse 12, 80331 München, Germany
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg
Geschäftsführer: Graham Law, Christine Elizabeth Flores
(Sorry; I'm legally required to add this exciting detail to emails. Bleh.)


On Thu, Jan 9, 2014 at 9:14 AM, Mark Nottingham <mnot@mnot.net> wrote:

> Doesn't relying on CORS assume that sensitive data will never be available
> cross-origin?
>
> Sent from my iPhone
>
> On 9 Jan 2014, at 3:26 pm, Michal Zalewski <lcamtuf@coredump.cx> wrote:
>
> >> What is the mitigation that you're agreeing with, Michal? Only
> performing
> >> integrity checks on resources delivered with explicitly public
> cache-control
> >> or CORS headers?
> >
> > Well, Eduardo's take is that we should just require CORS and not dance
> > around it. Maybe that would work, although it does require explicit
> > cooperation of the third-party site that hosts a particular download,
> > has a copy of jQuery, etc. I'd imagine this won't always be painless.
> >
> > An alternative would be to unconditionally fail if integrity= is
> > specified and none of the following three conditions are met:
> >
> > 1) The subresource is same-origin with the requestor,
> >
> > 2) The subresource is publicly cacheable by proxies (either due to
> > implicit caching rules, or due to Cache-Control),
> >
> > 3) There is a CORS header that explicitly permits this subresource to
> > be accessed across origins.
> >
> > /mz
>