Software Engineering Institute

Sun Java WebStart is a technology for launching stand-alone Java applications. On Microsoft Windows systems, Java WebStart is provided by the program javaws.exe, which is included with the Sun Java Runtime Environment (JRE). Java WebStart operates by processing a JNLP file, which is an XML document that contains information about the Java application to execute. The Sun JRE installer configures Internet Explorer and Netscape Navigator to automatically open JNLP files without any user interaction.

Java WebStart contains a stack buffer overflow in the handling of JNLP files. This vulnerability can be exploited to execute arbitrary code as the result of opening a specially-crafted JNLP file, which can occur as the result of viewing a malicious web site. We have received reports that this vulnerability is being actively exploited.

By convincing a user to open a specially-crafted JNLP file, a remote, unauthenticated attacker may be able to execute arbitrary code on a vulnerable system. This may occur as the result of viewing a specially-crafted web page.

Apply an update
This issue is addressed in the following Java versions:

• JDK and JRE 6 Update 5
• JDK and JRE 5.0 Update 15
• SDK and JRE 1.4.2_17

Delete the Windows file association for JNLP files
The file association for JNLP files on windows systems can be removed by deleting the following registry keys:
HKLM\Software\Classes\.jnlp
HKLM\Software\Classes\MIME\Database\Content Type\application/x-java-jnlp-file
HKLM\Software\Classes\JNLPfile
Disable the Java WebStart ActiveX control in Internet Explorer
The Java WebStart ActiveX control can be disabled in Internet Explorer by setting the kill bit for the following CLSID:

{5852F5ED-8BF4-11D4-A245-0080C6F74284}
More information about how to set the kill bit is available in Microsoft Support Document 240797. Alternatively, the following text can be saved as a .REG file and imported to set the kill bit for this control:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\ActiveX Compatibility\{5852F5ED-8BF4-11D4-A245-0080C6F74284}]
"Compatibility Flags"=dword:00000400