[VulnWatch] EEYE: Sun Java WebStart JNLP Stack Buffer Overflow Vulnerability

From: eEye Advisories (Advisories@private)
Date: Mon Jul 09 2007 - 14:09:44 PDT

Sun Java WebStart JNLP Stack Buffer Overflow Vulnerability

Release Date:
July 5, 2007

Date Reported:
Jan 19, 2007

High (Remote Code Execution)

Sun Microsystems

Systems Affected:
Java Runtime Environment 6 Update 1, and earlier
Java Runtime Environment 5 Update 11, and earlier

[Sun is one of the few companies that is still unable to coordinate the
simultaneous release of security patches, this organizational failure
puts customers at undue risk. Sun first released a patch for this
vulnerability on June 28th for Java Runtime Environment 5, as Update 12.
Now over a week later Sun has finally released the rest of the Java 6
updates for affected systems. People have potentially had over a week to
develop exploits for this vulnerability before Sun finally released a
patch for Java 6, which is the current download of Java. eEye strongly
recommends people install this patch as soon as possible. Hopefully in
the future Sun will be able to bring their security and development
process out of the dark ages. -Marc Maiffret]

eEye Digital Security has discovered a stack buffer overflow in Java
WebStart, a utility installed with Java Runtime Environment for the
purpose of managing the download of Java applications.  By opening a
malicious JNLP file, a user's system may be compromised by arbitrary
code within the file, which executes with the privileges of that user.

A web-based attack conducted through Internet Explorer may succeed
without the use of ActiveX or scripting, and without any additional user
interaction other than viewing a web page, if the web server indicates a
Content-Type of "application/x-java-jnlp-file" when serving up the
malicious JNLP file.  In such a case, a ".jnlp" file extension is not

Technical Details:
javaws.exe is responsible for extracting download instructions from JNLP
files, which are essentially XML.  The jnlp element in the JNLP file
contains a codebase attribute.  This attribute is later copied (via
sprintf) into a 1K buffer, where is it also prepended with the path to
the user's temp directory.  As there is no length validation imposed
prior to sprintf, the stack-based buffer can be overflowed by whatever
is passed into the codebase.  The one restriction placed on the input is
that any multi-byte characters are converted into a single '0xFF', so
only characters 0x01 through 0x7F are permissible.

To work around this vulnerability, if you are not actively using Java
WebStart, remove the .jnlp content type association in your registry:
- HKLM:Software\Classes\.jnlp
- HKLM:Software\Classes\JNLPfile
- HKLM:Software\Classes\MIME\Database\Content

By deleting or mutilating these registry keys, Java WebStart will no
longer be used to open .jnlp files, thereby mitigation this

Retina - Network Security Scanner has been updated to identify this
Blink - Unified Client Security has proactively protected from this
vulnerability since its discovery.

Vendor Status:
Sun Microsystems has released a patch for this vulnerability. 
JRE 5 Update 12 is available at:
JRE 6 Update 2 is available at:

Daniel Soeder

Related Links:
Retina - Network Security Scanner - Free Trial:
Blink - Unified Client Security Personal - Free For Home Use:
Blink - Unified Client Security Professional - Free Trial:

Derek for his heap clutter and counting idea.  My homies in TX.
Panzarotti.  McSlibin keep on rocking.  Talis and Reverse - miss you

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