W3C home > Mailing lists > Public > public-webappsec@w3.org > July 2014

Re: [MIX] Consider all CORS requests "active"

From: Mike West <mkwst@google.com>
Date: Thu, 10 Jul 2014 14:39:38 +0200
Message-ID: <CAKXHy=fGpMpnPCcLBnfoRTdutA5GkBdTp3wKHPXVe4n+Pcf4Wg@mail.gmail.com>
To: Jake Archibald <jaffathecake@gmail.com>
Cc: "public-webappsec@w3.org" <public-webappsec@w3.org>
The general idea sounds quite plausibly workable to me.

That said:

On Thu, Jul 10, 2014 at 1:08 PM, Jake Archibald <jaffathecake@gmail.com> wrote:
> http://w3c.github.io/webappsec/specs/mixedcontent/#requirements-script
> Currently, XHR & EventSource specifically fail when requesting insecure
> content.

This section notes that we'd throw exceptions synchronously when we
can determine that a request would be blocked. That is, if XHR
requests an HTTP resource on an HTTPS page, we'd fail the call to

I think we'd still want to do that.

> This could be replaced with a general rule that CORS checks to HTTP
> always fail. This also covers usually passive content that becomes active
> via CORS, eg <img crossorigin>.

We should totally try this out. It's another nice way to subdivide
images into bits that might be blockable.

Blink is now blocking mixed <picture> and <img srcset>, by the way.

> This means font requests to http would also fail, they could be given an
> exception if needed.

We're already blocking mixed font requests in Blink. Let's not make an

> importScripts('http://...'); - fails
> fetch('http://...'); - fails
> cache.add('http://...'); - fails
> …as they're all CORS dependant.

Yup, let's block these.

> fetch('http://...', {mode: 'no-cors'});
> cache.add(new Request('http://...', {mode: 'no-cors'}));
> …these will give back a tainted response. Usual rules can apply if they're
> used to satisfy requests to <script>, <img> etc.

Why would we allow these requests? Wouldn't we want to block them as well?

Mike West <mkwst@google.com>
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Received on Thursday, 10 July 2014 12:40:26 UTC

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