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iDefense Security Advisory 03.25.09
http://labs.idefense.com/intelligence/vulnerabilities/ 
Mar 25, 2009

I. BACKGROUND

Pack200 is a compression method introduced by Sun in the 1.5 release of
the JRE. It is used to compress JAR files, and is optimized for the
compression of Java class files. A Java applet can be compressed using
the pack200 tool, and if the browser plugin supports the pack200-gzip
encoding it will pass the compressed JAR file to the JRE for unpacking.
For more information, see the vendor's site at the following links.

http://www.sun.com/java/ 
http://java.sun.com/j2se/1.5.0/docs/guide/deployment/deployment-guide/pack200.html 

II. DESCRIPTION

Remote exploitation of an integer overflow vulnerability in Sun
Microsystems Inc.'s Java Runtime Environment (JRE) could allow an
attacker to execute arbitrary code with the privileges of the current
user.

The vulnerability occurs during decompression when, to calculate the
size of a heap buffer, the code manipulates several integers in the
file. The bounds of these values are not checked, and the arithmetic
operations can overflow. This results in an undersized buffer being
allocated, which leads to a heap-based buffer overflow.

This vulnerability is similar to a previous iDefense vulnerability in
the JRE Pack200 code, and is due to an incomplete fix of the previous
vulnerability.

III. ANALYSIS

Exploitation allows attackers to execute arbitrary code in the context
of the currently logged-on user. To exploit this vulnerability, a
targeted user must load a malicious Web page created by an attacker. An
attacker typically accomplishes this via social engineering or injecting
content into compromised, trusted sites.

Exploitation of heap-overflow vulnerabilities on modern operating
systems can, at times, be difficult due to various heap integrity
protections; however, the Pack200 code uses a custom allocator that
does not contain such integrity checks. Labs testing has demonstrated
that code execution is possible on the Linux platform. A similar
methodology is likely to be successful on the Windows platform.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability in Sun
Microsystem Inc.'s JRE version 1.6.0_11 for Windows and Linux.
According to Sun, Pack200 was first introduced to JRE 1.5.0. The latest
version of JRE 1.5, 1.5.0_15, does contain the vulnerable code, but the
browser plugin does not handle Pack200 encoding. As such, exploitation
through the browser does not appear to be possible with JRE 1.5. This
vulnerability is different than the previously reported iDefense issue
with the Pack200 code.

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

Note: SDK and JRE 1.4.2 and 1.3.1 are not affected by this issue.

V. WORKAROUND

The library containing the vulnerability can be renamed, which will
prevent it from being loaded. This workaround will prevent users from
loading Pack200 format JAR files, and from using the pack/unpack tools
that come with the JRE; however, normal applets and Java applications
will continue to function correctly. The vulnerable library is called
"unpack" and can be found in:

"%SYSTEMDRIVE%\Program Files\Java\JAVA VERSION\bin\unpack.dll"

on Windows and in differing locations, dependent upon the
distribution/platform on Unix systems.

VI. VENDOR RESPONSE

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

http://sunsolve.sun.com/search/document.do?assetkey=1-66-254570-1 

VII. CVE INFORMATION

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

VIII. DISCLOSURE TIMELINE

01/09/2009  - Initial Contact
01/22/2009  - requested PoC
01/22/2009  - sent PoC
01/31/2009  - Vendor acknowledged PoC
02/05/2009  - Requested CVE from vendor
03/25/2009  - Coordinated Public Disclosure

IX. CREDIT

This vulnerability was reported to iDefense by regenrecht.

Get paid for vulnerability research
http://labs.idefense.com/methodology/vulnerability/vcp.php 

Free tools, research and upcoming events
http://labs.idefense.com/ 

X. LEGAL NOTICES

Copyright =A9 2009 iDefense, Inc.

Permission is granted for the redistribution of this alert
electronically. It may not be edited in any way without the express
written consent of iDefense. If you wish to reprint the whole or any
part of this alert in any other medium other than electronically,
please e-mail customerservice@idefense.com for permission. 

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
author nor the publisher accepts any liability for any direct,
indirect, or consequential loss or damage arising from use of, or
reliance on, this information.
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