[whatwg] Cross-origin JavaScript capability leak in showModalDialog

[Adam Barth]

On Thu, Jun 11, 2009 at 6:21 PM, Ian Hickson<ian at hixie.ch> wrote:
> On Thu, 28 May 2009, Adam Barth wrote:
>>
>> In Step 12 of
>> http://www.whatwg.org/specs/web-apps/current-work/#dom-showmodaldialog,
>> the auxiliary browsing context's return value is transfered from the
>> auxiliary browsing context to whichever script called showModalDialog
>> without regard for the origin of these two browsing contexts.  In most
>> situations, this will let the auxiliary browsing context XSS the caller
>> of showModalDialog.  Instead, we should perform the same origin checks
>> and subsequent transformations that we perform on the dialog arguments
>> in step 7.
>
> The return value is always just a string; why is this a problem? Surely
> it's more or less equivalent to handling a string passed from a foreign
> postMessage() call or some such.

Strings are fine.  I misread the spec.  I thought it was grabbing the
returnValue JS value, not the DOM value.  This is just an
implementation bug then.  :)

> Note that returnValue can also be used as a cross-origin communication
> mechanism here; if this is a problem, do you want to track the origin of
> the setter and treat it as "" if the origin differs?

No, I don't think that's necessary.

Thanks,
Adam