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

["Hill, Brad" <[e-mail]>]

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.
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(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.