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.
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.
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.
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.
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:
Renaming this file to splashscreen.dll.bak will prevent it from being loaded.
Sun Microsystems 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.
10/01/2008 Initial Vendor Notification
11/05/2008 Initial Vendor Reply
11/25/2008 Additional Vendor Feedback
12/02/2008 Coordinated Public Disclosure
This vulnerability was reported to iDefense by regenrecht.
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