Opera Images (GM#004-OP)

[GreyMagic Software <security () greymagic com>]

GreyMagic Security Advisory GM#004-OP
=====================================

By GreyMagic Software, Israel.
04 Feb 2003.

Available in HTML format at http://security.greymagic.com/adv/gm004-op/.

Topic: Opera Images.

Discovery date: 29 Jan 2003.

Affected applications:
======================

Opera 7 (final).


Introduction:
=============

Opera recently released a new version of its browser. 

Opera 7, just like any other browser, supports a considerable amount of
image formats. Images are normally embedded in HTML documents but they can
also be accessed directly via the browser. 


Discussion: 
===========

By examining the HTML Opera produces when it displays a single image, it
becomes obvious that Opera doesn't bother to do any formatting on the
provided URL. Luckily though, Opera automatically encodes most characters in
the URL, so access to other domains via this flaw becomes impossible. 

However, URLs to local files (file:// protocol) do not get encoded and
therefore cannot evade the very basic form of XSS:
file://path/to/image.jpg?">Arbitrary HTML here. 

And to make this even more comfortable for attackers, Opera provided an easy
way to refer to its own installation directory - file://localhost/. So
instead of searching for default images in the OS, an attacker can simply
refer to file://localhost/images/file.gif, one of the few images Opera ships
by default, and enjoy the following abilities: 

* Read any file on the user's file system. 
* Read the contents of directories on the user's file system. 
* Read emails written or received by M2, Opera's mail program. 
* And more... 

Note: the same applies to embeddable media, such as SWF. 


Exploit: 
========

open("file://localhost/images/file.gif?\"><script>alert(location.href);</scr
ipt>","",""); 


Demonstration:
==============

We put together two proof-of-concept demonstrations: 

* Simple: Demonstrates how a single local image can be exploited. 
* GreyMagic Opera Disk Explorer: Browse your entire file system using this
explorer-like tool, which takes advantage of this vulnerability in order to
access local resources. 

They can both be found at http://security.greymagic.com/adv/gm004-op/.

Solution: 
=========

Until a patch becomes available, disable Javascript by going to: File ->
Preferences -> Multimedia, and uncheck the "Enable JavaScript" item. 


Tested on: 
==========

Opera 7 NT4.
Opera 7 Win98.
Opera 7 Win2000.
Opera 7 WinXP.


Disclaimer: 
===========

The information in this advisory and any of its demonstrations is provided
"as is" without warranty of any kind. 

GreyMagic Software is not liable for any direct or indirect damages caused
as a result of using the information or demonstrations provided in any part
of this advisory. 


Feedback: 
=========

Please mail any questions or comments to security () greymagic com. 

- Copyright © 2003 GreyMagic Software.