iDefense Security Advisory 08.04.09
http://labs.idefense.com/intelligence/vulnerabilities/
Aug 04, 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 plug-in 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 when reading the header of the Pack200
compressed Jar file during decompression. To calculate the size of a
heap buffer, the code multiplies and adds several 32-bit integers. 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 two previous iDefense Exclusives in the
JRE Pack200 code and is due to an incomplete fix of the previous
vulnerabilities.

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.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability in Sun
Microsystems Inc.'s JRE version 1.6.0_13 for Windows and Linux. This
vulnerability is different than the two previously reported iDefense
Exclusives in the Pack200 code.

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 Microsystems 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=1-66-263488-1

VII. CVE INFORMATION

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

VIII. DISCLOSURE TIMELINE

04/09/2009  - Initial Contact
04/13/2009  - PoC Requested
04/13/2009  - Clarification Requested
04/13/2009  - PoC Sent
04/21/2009  - Clarification Sent
07/22/2009  - Tentative Disclosure set for July 27, 2009
07/22/2009  - Requested CVE
07/22/2009  - Sun delays disclosures
07/28/2009  - Tentative Disclosure set for August 3rd, 2009
08/04/2009  - Coordinated public disclosure

IX. CREDIT

This vulnerability was reported to iDefense by regenrecht.

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X. LEGAL NOTICES

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.
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