iDefense Security Advisory 03.26.09: Sun Java Web Start (JWS ) GIF- Decoding Heap Corruption Vulnerability

From: iDefense Labs <>
Subject: iDefense Security Advisory 03.26.09: Sun Java Web Start (JWS ) GIF- Decoding Heap Corruption Vulnerability

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iDefense Security Advisory 03.25.09
Mar 25, 2009


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 the browser. In order
to accomplish this, the Java Network Launching Protocol (JNLP) is used
to communicate with the JWS process. This is done by referencing a
.jnlp file from the Web page, which is then requested and forwarded to
the JWS application. This XML-based file contains various parameters
that describe the Java application to be run.


Remote exploitation of a heap corruption vulnerability in Sun
Microsystems Inc.'s Java Web Start could allow an attacker to execute
arbitrary code with 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 a JNLP file to provide its own splash logo. This allows
an attacker to pass an arbitrary GIF file to the splash logo parsing
code to trigger the vulnerability.


Exploitation of this vulnerability results in the execution of arbitrary
code with the privileges of the user running JWS. There are several ways
to exploit this vulnerability. The most common exploitation vector is
through the browser. By persuading a user to follow a link (or by
compromising a trusted site), the vulnerability can be exploited by
simply viewing a webpage. It would also be possible for an attacker to
e-mail a JNLP 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.


iDefense has confirmed the existence of this vulnerability in Java Web
Start version 1.6_11 on Windows and Linux. Previous versions may also
be affected.

Sun Microsystems reports that the vulnerability can occur in the
following Java SE and Java SE for Business releases for Windows,
Solaris, and Linux:

    * JDK and JRE 6 Update 12 and earlier
    * JDK and JRE 5.0 Update 17 and earlier

and in the following Java SE for Business release for Windows, Solaris,
and Linux:

    * SDK and JRE 1.4.2_19 and earlier

and in the following Java SE release for Windows and Solaris:

    * SDK and JRE 1.3.1_24 and earlier


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. If a user specifically
selects the Java Web Start application to open the JNLP file, however,
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. One such location is:

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

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


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


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


02/18/2009  - Initial Contact
02/18/2009  - PoC Requested
02/19/2009  - PoC Sent
03/10/2009  - Disclosure Date Set
03/25/2009  - Coordinated Public Disclosure


This vulnerability was reported to iDefense by regenrecht.

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Copyright  2009 iDefense, Inc.

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