Date: Thu, 22 Apr 2010 14:17:46 -0400
From: Dan Kaminsky <dan@...para.com>
To: T Biehn <tbiehn@...il.com>
Cc: Full disclosure <full-disclosure@...ts.grok.org.uk>
Subject: Re: IE8 img tag HiJacking

Also, Billy Hoffman has done a lot of fun work in this space, see
http://www.gnucitizen.org/blog/javascript-remoting-dangers/



2010/4/22 Dan Kaminsky <dan@...para.com>:
> Interesting use, using filesize to back into the actual CAPTCHA used for a
> given query.  Sneaky!
>
> So it's possible to read not only filesize, but image dimensions
> cross-domain.  I actually found a use for this -- it's a good way to
> exchange a small amount of data between sites that mutually distrust one
> another.  The reason for this is that images are pretty much the only
> resources that can be loaded cross-domain that won't have embedded script
> executed by a browser.
>
> (Side note:  At this point, you're probably thinking:  Vladimir just said
> that some browsers allow SVG to load via <img> -- and SVG can embed script
> with nothing but a script tag  and a smile!  Doesn't this mean a bunch of
> sites are in trouble?
>
> Turns out, no, not as far as I can tell anyway.  IE and Firefox both block
> <img> to SVG entirely, while Chrome, Safari, and Opera allow it.  But there
> appears to be a script firewall (or more accurately, a missing connection)
> between <img>-loaded SVG and the script engine.  Static SVG renders just
> fine, but don't expect it to do anything unless you top-level nav, inline,
> or use something like embed.)
>
> Back to image dimensions, it turns out that this information channel cannot
> be closed; even if the dimensions of the object itself couldn't be queried,
> the XY positioning of the objects *around* the imported images must be both
> queryable and dependent on image properties.
>
> I was curious however if img.fileSize would leak filesizes of non-image
> content.  Doesn't look like it does -- undefined in everything but IE, -1 in
> IE.
>
>
> 2010/4/22 T Biehn <tbiehn@...il.com>
>>
>> It could be used as a technique for defeating the login images used as
>> "two-factor-authentication" by some online services.
>> The application of using filesize to fingerprint an image is somewhat
>> novel. This is a decidedly 'old' vector, though.
>>
>> -Travis
>>
>> 2010/4/21 Владимир Воронцов <vladimir.vorontsov@...ec.ru>
>>>
>>> Hello Full disclosure!
>>>
>>> Once again, unwinding theme HiJacking found a fun way to get the very
>>> least information about the target resource when the user is located at
>>> the
>>> attacker.
>>>
>>> Already crocked <img> tag opens new opportunities using the method
>>> fileSize, described here:
>>> http://msdn.microsoft.com/en-us/library/ms533752
>>> (v = VS.85). Aspx
>>>
>>> Consider a simple example - a Web application after authentication
>>> provides some sort of picture for the user, for example:
>>>
>>> http://example.com/getImage.php?image=myAvatar
>>>
>>> The attacker, knowing this can create a page to read:
>>>
>>> <img id="onsec" src="http://example.com/getImage.php?image=myAvatar">
>>>
>>> <input type="button" onclick="if (onsec.fileSize> 0) (alert ('authorized
>>> on example.com') else (alert ('not authorized on example.com')}">
>>>
>>> Thus, the attacker learns the simplest case, whether the target user
>>> access to example.com.
>>>
>>> Continuing the theme, I want to note that in some cases, can obtain
>>> additional information from the very values of the size of the picture.
>>> It
>>> can be any logical information Web applications, say, the same script can
>>> show administrators a picture of the same size, and users - of another.
>>> Thus, we obtain the user rights. And so on.
>>>
>>> I'd like to return the size of the method is not only "valid" images, but
>>> also HTML pages, JSON, etc. But, unfortunately, does not work. Maybe, of
>>> course, there are exceptions, call to investigate the matter.
>>>
>>> I have some thoughts on the study of vector images in XML format, because
>>> HTML is often valid XML, and then ...
>>>
>>> Check for the test version IE9, but he did not support SVG inside tag
>>> <img>, but only as a separate tag.
>>>
>>> Works in IE8, in Opera 10.52 does not work on check writing, if not
>>> difficult.
>>>
>>> Original at russian language: http://oxod.ru/?p=113
>>>
>>> --
>>> Best regards,
>>> Vladimir Vorontsov
>>> ONsec security expert
>>>
>>> _______________________________________________
>>> Full-Disclosure - We believe in it.
>>> Charter: http://lists.grok.org.uk/full-disclosure-charter.html
>>> Hosted and sponsored by Secunia - http://secunia.com/
>>
>>
>>
>> --
>> FD1D E574 6CAB 2FAF 2921  F22E B8B7 9D0D 99FF A73C
>> http://pgp.mit.edu:11371/pks/lookup?search=tbiehn&op=index&fingerprint=on
>> http://pastebin.com/f6fd606da
>>
>> _______________________________________________
>> Full-Disclosure - We believe in it.
>> Charter: http://lists.grok.org.uk/full-disclosure-charter.html
>> Hosted and sponsored by Secunia - http://secunia.com/
>
>

_______________________________________________
Full-Disclosure - We believe in it.
Charter: http://lists.grok.org.uk/full-disclosure-charter.html
Hosted and sponsored by Secunia - http://secunia.com/

Powered by blists - more mailing lists