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iDefense Security Advisory 03.26.09: Sun Java Web Start (JWS ) PNG Decoding Integer Overflow 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. For more information, see
the vendor's site found at the following link.



Remote exploitation of an integer overflow 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 PNG file to the splash logo parsing

The vulnerability occurs when parsing a PNG file used as part of the
splash screen. When parsing the image, several values are taken from
the file and used in an arithmetic operation that calculates the size
of a heap buffer. This calculation can overflow, which results in an
undersized buffer being allocated. This buffer is later overflowed with
data from the file.


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

Note: JDK and JRE 5.0, SDK and JRE 1.4.2 and 1.3.1 are not affected.


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 discovered by regenrecht.

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Copyright © 2009 iDefense, Inc.

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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
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