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[whatwg] <object> behavior

From: Ian Hickson <ian@hixie.ch>
Date: Sun, 18 Oct 2009 19:47:26 +0000 (UTC)
Message-ID: <Pine.LNX.4.62.0910181924290.26598@hixie.dreamhostps.com>
On Sun, 18 Oct 2009, Ben Laurie wrote:
> On Sun, Oct 18, 2009 at 5:37 AM, Ian Hickson <ian at hixie.ch> wrote:
> > On Fri, 16 Oct 2009, Ben Laurie wrote:
> >> > On Thu, 6 Aug 2009, Andrew Oakley wrote:
> >> >>
> >> >> - Should the type attribute take precedence over the Content-Type
> >> >> header?
> >> >
> >> > No, I believe what the spec says here is the preferred behaviour.
> >> > Unless this is incompatible with legacy content, we should try to move
> >> > towards this behaviour.
> >>
> >> I realise this is only one of dozens of ways that HTML is unfriendly to
> >> security, but, well, this seems like a bad idea - if the page thinks it
> >> is embedding, say, some flash, it seems like a pretty bad idea to allow
> >> the (possibly untrusted) site providing the "flash" to run whatever it
> >> wants in its place.
> >
> > If the site is untrusted, yet you are letting it run flash, then you've
> > lost already. Flash can inject arbitrary JS into your page.
> 
> Perhaps I am failing to understand, but if I embed anything from an
> untrusted site, then it can choose what type it is - so how would I
> prevent it running Flash?

You can't exclude one type and allow others, but if you want a very 
specific type used for a plugin, you can use <embed>. If you just want to 
allow the untrusted site to do anything, but in their own security context 
so it can't harm your site, use <iframe>.


> > If you are worried about security, I recommend using <iframe>. The new 
> > sandbox="" feature will help even more, once implemented.
> 
> I am worried about security, and I recommend using Caja - but Caja still 
> has to output valid HTML/CSS/JS...

I don't understand the problem.


> > On Fri, 16 Oct 2009, Boris Zbarsky wrote:
> >>
> >> This cuts both ways. ?If a site allows me to upload images and I 
> >> upload an HTML file with some script in it and tell it it's a GIF 
> >> (e.g. via the name) an then put an <object type="text/html" 
> >> data="http://this.other.site/my.gif"> on my site... ?then I just 
> >> injected script into a different domain if we let @type override the 
> >> server-provided header.
> >>
> >> This is, imo, a much bigger problem than that of people embedding 
> >> content from an untrusted site and getting content X instead of 
> >> content Y, especially because content X can't actually access the 
> >> page that contains it, right?
> >
> > Indeed.
> 
> You just said it could, above.

The example Boris mentioned was HTML. Embedded HTML is always 
origin-blocked. The example I mentioned earlier was Flash. Flash runs in 
the context of the embedder page.

HTH,
-- 
Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'
Received on Sunday, 18 October 2009 12:47:26 UTC

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