W3C home > Mailing lists > Public > public-webappsec@w3.org > January 2013

Re: CSP interacting with HSTS

From: Adam Barth <w3c@adambarth.com>
Date: Tue, 15 Jan 2013 00:07:50 -0800
Message-ID: <CAJE5ia_vALYS5RfNbBmbthrRE38-bzFFmNrg9i42=N077Pv5fw@mail.gmail.com>
To: Ian Melven <imelven@mozilla.com>
Cc: public-webappsec <public-webappsec@w3.org>
Won't the same issue occur if a web site starts redirecting http
traffic to https?  HSTS is just a browser-side redirect.


On Mon, Jan 14, 2013 at 2:15 PM, Ian Melven <imelven@mozilla.com> wrote:
> Hi,
> In https://bugzilla.mozilla.org/show_bug.cgi?id=826805 , Brian Smith brought
> up a possible problematic interaction with CSP and HSTS :
> "Because of HSTS, which can cause of to automatically redirect HTTP requests to HTTPS, we need to interpret a "http:"
> scheme-source as "http: https:", and we need to interpet a host-source of the form "http://host[:port]" as "http://host[:port] https://host:[port]".
> Otherwise, if we get the CSP directive before the site turns on HSTS, and then later the site turns on HSTS,
> the site will break. In particular, consider the case where we've cached a page in the HTTP response cache with
> a CSP with scheme-sources of the form "http:", which references sub-resources (using http:// URLs) of a
> newly-HSTS-enabled site. Without this change, that page would be broken until it is evicted from the cache,
> because HSTS will rewrite the http:// URLs as https:// URLs, and then CSP will block the https:// content from loading."
> regardless of caching, for example if http://a.com contains images from
> http://b.com and has a CSP of image-src: http://b.com , if b.com turns on
> HSTS, this will break.
> other places in Gecko explicitly handle this situation - I'm informed that websockets for example
> will generally not follow a redirect without an implemented redirect header, EXCEPT in the case
> where the redirect is to an identical URL with a wss: scheme instead of a ws: scheme.
> thoughts/comments welcome !
> thanks,
> ian
Received on Tuesday, 15 January 2013 08:08:52 UTC

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