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[whatwg] Revising the content handling logic of <object> and <embed>

From: Michael A. Puls II <shadow2531@gmail.com>
Date: Mon, 07 Mar 2011 15:49:13 -0500
Message-ID: <op.vrzqsbj01ejg13@sandra-svwliu01>
On Mon, 07 Mar 2011 15:11:03 -0500, Michal Zalewski <lcamtuf at coredump.cx>  

> Hi folks,
> The HTML4 spec said that on <object> and <embed> tags, Content-Type
> overrides type=. All browser vendors implemented a different behavior,
> however, where type= almost always overrides Content-Type.
> Plugin vendors, in turn, missed that "almost" part, built extensive
> security mechanisms, and promoted use cases where one site can embed
> Flash movies, PDF documents, simple multimedia, and so on, from
> another, untrusted source without suffering substantial security
> consequences. For example, Flash exposes allowScriptAccess,
> allowNetworking, and allowFullScreen parameters that can be used to
> sandbox the loaded content:
> <object data="http://somewhere_funny/"  
> type="application/x-shockwave-flash">
> <param name="allowScriptAccess" value="never">
> <param name="allowNetworking" value="never">
> <param name="allowFullScreen" value="never">
> </object>
> People embraced this approach in web discussion forums, on online blogs,  
> etc.
> Unfortunately, there is the "almost" part: in some originally
> undocumented cases, browsers permit the attacker to override explicit
> type= based on URL file extensions, content sniffing, or Content-Type.
> This makes the aforementioned popular use case dangerous, because any
> site that wishes to embed a security-restricted Flash movie may end up
> embedding a Java applet instead, and Java has unconditional access to
> the DOM of the embedding page via DOMService.
> While it can be argued that it's the websites and plugin vendors that
> are doing it wrong, the issues with HTML4 spec and actual browser
> behavior contributed to it, and it may be prudent to fix the mess.
> HTML5 spec makes an attempt to explicitly sanction the current
> behavior, where neither the embedding nor the hosting party have
> control over how the content will be displayed, in the specification
> for the <object> element. Given the aforementioned situation, I think
> this is harmful and needs to be revised.
> In my opinion, the preferred outcome would be to make type=
> authoritative when specified, or provide an alternative way of
> ensuring specific routing of the retrieved content on markup level. In
> addition, to resolve existing problems with non-plugin content being
> interpreted as plugin data (e.g.
> http://xs-sniper.com/blog/2008/12/17/sun-fixes-gifars/), it would also
> be prudent to provide servers a way to demand rendering only if
> Content-Type provided by the server, and type= in the markup, match.
> Thoughts?

I agree and for the same reasons as you.

Like Boris, I think one should be able to specify this via an attribute.

Received on Monday, 7 March 2011 12:49:13 UTC

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