W3C home > Mailing lists > Public > public-webappsec@w3.org > November 2012

Re: UI Safety Obstruction check and transforms

From: David Lin-Shung Huang <linshung.huang@sv.cmu.edu>
Date: Wed, 28 Nov 2012 12:02:58 -0800
Message-ID: <CAGiwpwjBpdxdAGfuSK0c3nA9ETmrtw6xzKxVbuGE9-XviWRwcg@mail.gmail.com>
To: Fred Andrews <fredandw@live.com>
Cc: "public-webappsec@w3.org" <public-webappsec@w3.org>
Hi Fred,

The idea of providing a force-topmost (or force-opaque, etc) attribute or
style is actually an interesting approach and has been brought up a couple
of times by other researchers. However, as far as I know, it is not simple
in practice for the UA to guarantee that a widget bypasses all transforms
imposed by parents, while rendering existing webpages properly. One thing
to keep in mind is that altering the appearance of webpages that are
non-attacks would be unacceptable to major websites and browser vendors. We
should also be concerned that such a feature might be abused by widgets/ads
to override pixels on the parent page maliciously.

I think worth pointing out is that the obstruction detection
approach doesn't require modifying the default appearance of existing
webpages, and taking screenshots is rather straightforward to implement
while agnostic to new HTML5/CSS/SVG features (proven feasible in ClearClick
and InContext).


On Wed, Nov 28, 2012 at 3:45 AM, Fred Andrews <fredandw@live.com> wrote:

> Hi David,
> Thank you for the suggestion.  I guess if a widget received an event with
> this flag set it could redirect to a confirmation page in which it was not
> framed.  However it is not clear if the event flag could be used to bypass
> a transform imposed on a widget by its parent to avoid the obstruction
> check failure.
> For example, consider a social widget that has simply been scaled so that
> it fails an obstruction check.  A reasonable default action for the UA
> could be to present the widget unscaled when hovering over it.  The UA
> needs to compute this unscaled view anyway for comparison so it may not be
> a big extra step.  It may well be that the spec. already allows a UA to do
> this, but it might be handy to have an event sent to the widgets parent
> document to give it the option to present the widget unscaled itself, and
> perhaps this could even link into the CSS to allow for 'unobstructed'
> styling when needed.
> BTW: your papers are very good resources, thanks.
> cheers
> Fred
> ------------------------------
> Date: Wed, 28 Nov 2012 00:22:33 -0800
> From: linshung.huang@sv.cmu.edu
> To: fredandw@live.com
> CC: public-webappsec@w3.org
> Subject: Re: UI Safety Obstruction check and transforms
> Hi Fred,
> In Section 4 of the draft, the proposed "unsafe" boolean flag in the
> UIEvent object signals the webpage that obstruction was detected by the
> UA (whether it was caused by an attack or a benign transform). This allows
> the webpage to react with an extra confirmation dialog, or implement other
> custom fallbacks.
> Thanks,
> David
> On Wed, Nov 21, 2012 at 2:21 AM, Fred Andrews <fredandw@live.com> wrote:
> The issue of transforms applied to an element receiving an event has been
> discussed before and the opinion offered was that transformed elements are
> not supported.   Given that an element needs to be non-transformed to pass
> the obstruction check perhaps it would be appropriate to support elements
> being presented without transforms when about to receive events.  The use
> case would be to support rich UI designs that still offer UI safety.
> For example, consider a UI that docks social widgets at the side of a page
> and scales them down and applies a perspective transform for effect.  If
> input protection has been requested then these widgets would need to be
> presented unscaled and without the transform to pass the obstruction check.
> Could a UA recognize the issue and present the element in a little popup
> when hovering over it, or could the UA apply an extra confirmation step
> when an obstruction is detected and present the element unscaled and
> without the transform for confirmation?   If so then perhaps an
> implementation note of the possibilities would be appropriate.
> Might it be appropriate to signal an event that the webpage could use to
> implement such presentation itself, with a default left to the UA?  If so
> then the spec. would presumably need to define this event.
> For the case of a docked widget, a two step process would not be an
> unreasonable UI design, and is there enough support for webpage designers
> to be able to implement such a design.
> cheers
> Fred
Received on Wednesday, 28 November 2012 20:03:32 UTC

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