Re: [websec] X-Frame-Options EBNF bug at Mozilla

Julian Reschke <julian.reschke@gmx.de> Wed, 13 February 2013 10:00 UTC

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Date: Wed, 13 Feb 2013 11:00:09 +0100
From: Julian Reschke <julian.reschke@gmx.de>
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To: "Hill, Brad" <bhill@paypal-inc.com>
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Cc: IETF WebSec WG <websec@ietf.org>
Subject: Re: [websec] X-Frame-Options EBNF bug at Mozilla
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On 2013-02-11 23:09, Hill, Brad wrote:
> This bug at Mozilla was recently brought to my attention:
>
> https://bugzilla.mozilla.org/show_bug.cgi?id=836132
>
> It seems to indicate that the specified EBNF of using a colon between "ALLOW-FROM" and the URI is not the actual behavior of most user agents that implement that functionality.
>
> Perhaps we should update this to reflect the predominant implementation in the field. (Internet Explorer's)
>
> -Brad

Removing the colon (*not* making it optional) would also be consistent 
with the description in 
<http://blogs.msdn.com/b/ieinternals/archive/2010/03/30/combating-clickjacking-with-x-frame-options.aspx>.

Note that the ABNF needs to be updated to RFC 5234 syntax anyway, and 
that it should only describe the header field value, such as:

X-Frame-Options = "DENY"
                 / "SAMEORIGIN"
                 / ("ALLOW-FROM" RWS URI)

RWS = <RWS, as defined by HTTPbis, P1>
URI = <URI, as defined in RFC3986, Section 3>

(we may want to discuss restricting URI to scheme + authority, though).

Best regards, Julian