Re: [websec] Richard Barnes' Discuss on draft-ietf-websec-x-frame-options-09: (with DISCUSS and COMMENT)

[Richard Barnes <[e-mail]>]

Safari also renders the innermost frame.


On Mon, Aug 19, 2013 at 3:31 PM, Hill, Brad <[e-mail]> wrote:

> I received a question as to whether all browsers really implement the
> top-level only check, or if any do an immediate parent or ancestor walk.  I
> could guess, but I'd rather test.  Here's a test case for public use:
>
> http://webappsec-test.info/~bhill2/XFO/XFO_Top.html
>
> I checked the latest IE, Chrome, Opera and Firefox and they all render the
> innermost frame. (don't have a Safari instance handy at the moment to test
> but welcome others' reports)
>
> -Brad
> ________________________________________
> From: Hill, Brad
> Sent: Friday, August 16, 2013 4:44 PM
> To: Richard Barnes; The IESG
> Cc: [e-mail]; [e-mail];
> [e-mail]
> Subject: RE: [websec] Richard Barnes' Discuss on
>  draft-ietf-websec-x-frame-options-09:   (with DISCUSS and COMMENT)
>
> Additional comments inline.
> ________________________________________
>
>
> (D3) Shouldn't ALLOW-FROM be followed by an origin, not a URI?  In other
> words, what does it mean to send "X-Frame-Options: ALLOW-FROM
> https://example.com/this/is/a/path?query#fragment"?
>
> [Hill, Brad] Agreed.
>
>
> (D3) In the ALLOW-FROM: what does "top level context" mean?  Do you
> really mean the top level here, as opposed to the next one up?  For
> example, suppose A loads B in an iframe, and B loads C, and then C sends
> an X-Frame-Options header with ALLOW-FROM.  Is the ALLOW-FROM origin
> compared to B or A?  In either case, you should also note the attacks
> that remain.  For example, if the answer is B, then B needs to use
> X-Frame-Options as well, or else, A can maliciously frame A within B.  Or
> if the answer is A, then C is trusting A not to load any malicious
> intermediate frames B.
>
> [Hill, Brad]  This really does mean the top/final origin value in a frame
> ancestor
> chain walk.  Browsers have implemented X-Frame-Options to check the
> Origin context that is topmost in the window or tab.  (the _top target,
> representing the full, original browsing context, not just the immediate
> parent frame)  This could be clarified perhaps, but is not incorrect.
>
>