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iDefense Security Advisory 12.02.08
https://labs.idefense.com/intelligence/vulnerabilities/
Dec 02, 2008

I. BACKGROUND

Java Web Start (JWS) is a framework built by Sun that is used to run
Java applications outside of the browser. It is distributed with the
Java Runtime Environment (JRE) installation. JWS is typically launched
by clicking on a link in the browser, and results in a separate process
being started that is not tied to the JVM inside of the browser. A file
contains various parameters that describe the Java application to be
run. For more information, see the vendor's site found at the following
link.

https://java.sun.com/javase/technologies/desktop/javawebstart/index.jsp

II. DESCRIPTION

Remote exploitation of a memory corruption vulnerability in Sun
Microsystems Inc.'s Java Web Start could allow an attacker to execute
arbitrary code with the privileges of the current user.

When JWS starts up, it displays a splash screen. By default, the image
displayed on this splash screen is a GIF file provided by Sun, but it
is possible for an attacker to pass an arbitrary GIF file to the splash
logo parsing code.

The vulnerability occurs when parsing this GIF file. The parsing code
does not correctly validate several values in the GIF header. This lets
an attacker write data outside of the bounds of an allocated heap
buffer, which can lead to the execution of arbitrary code.

III. ANALYSIS

Exploitation of this vulnerability results in the execution of arbitrary
code with the privileges of the user. There are several ways to exploit
this vulnerability. In Internet Explorer 6, after the user visits the
malicious web page, no further user interaction is needed. However, in
FireFox and Internet Explorer 7, the user will be presented with the
'File Open' confirmation dialog, and will have to accept opening the
file. It would also be possible for an attacker to e-mail an infected
file to a user, or place it on a shared network drive. In this
situation, a targeted user would need to manually open the file.

Even though the vulnerability is likely to be triggered through the
browser, the actual vulnerability occurs in the Web Start binary. Since
this vulnerability allows for relatively precise control of the area and
content of memory corrupted, reliable exploitation is possible.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability in Java Web
Start version 1.6_10 and 1.6_07 on Windows and Linux. Previous versions
may also be affected.

V. WORKAROUND

On Windows, it is possible to prevent automatic exploitation by double
clicking such a file, or opening it through the browser by removing the
file associations for JNLP files. However, if a user specifically
selects the Java Web Start application to open the JNLP file,
exploitation is still possible. This can be done by removing the
registry key for .jnlp in the 'HKEY_CLASSES_ROOT' registry hive.

An additional workaround which will prevent all exploitation attempts is
to rename the splashscreen library so that Java Web Start will not be
able to load it. This file is found in different locations depending on
the platform and installation choices, but one such location is:

C:\Program Files\Java\jre6\bin\splashscreen.dll

Renaming this file to splashscreen.dll.bak will prevent it from being
loaded.

VI. VENDOR RESPONSE

Sun Microsystems Inc. has released a patch which addresses this issue.
For more information, consult their advisory at the following URL.

https://sunsolve.sun.com/search/document.do?assetkey=1-66-244987-1

VII. CVE INFORMATION

A Mitre Corp. Common Vulnerabilities and Exposures (CVE) number has not
been assigned yet.

VIII. DISCLOSURE TIMELINE

10/01/2008  Initial Vendor Notification
11/05/2008  Initial Vendor Reply
11/25/2008  Additional Vendor Feedback
12/02/2008  Coordinated Public Disclosure

IX. CREDIT

This vulnerability was reported to iDefense by regenrecht.

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X. LEGAL NOTICES

Copyright © 2008 iDefense, Inc.

Permission is granted for the redistribution of this alert
electronically. It may not be edited in any way without the express
written consent of iDefense. If you wish to reprint the whole or any
part of this alert in any other medium other than electronically,
please e-mail customerservice@idefense.com for permission.

Disclaimer: The information in the advisory is believed to be accurate
at the time of publishing based on currently available information. Use
of the information constitutes acceptance for use in an AS IS condition.
~ There are no warranties with regard to this information. Neither the
author nor the publisher accepts any liability for any direct,
indirect, or consequential loss or damage arising from use of, or
reliance on, this information.
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