FreeBSD i386_set_ldt Integer Overflow Vulnerability

iDefense Security Advisory 09.23.06
http://www.idefense.com/intelligence/vulnerabilities/ 
Sep 23, 2006

I. BACKGROUND

FreeBSD is a modern operating system for x86, amd64, Alpha, IA-64, PC-98
and SPARC architectures. It's based on the UNIX operating system, BSD,
which was created at the University of California, Berkeley.  More
information can be obtained from the FreeBSD Project web site at
http://www.FreeBSD.org/ 

II. DESCRIPTION

Local exploitation of a input validation error in the FreeBSD Project's
i386_set_ldt() kernel implementation could allow attackers to create a
kernel panic, leading to a denial of service condition on the affected
computer.

III. ANALYSIS

Exploitation of this vulnerability would result in a denial of service
condition on the affected host.  There is a potential for arbitrary code
execution in kernel context due to the way this function manipulates
kernel heap memory. 

IV. DETECTION

iDefense has confirmed the existence of this problem in FreeBSD 5.5. It
is suspected that versions as early as 5.2 are also affected.

V. WORKAROUND

iDefense is not aware of any workaround for this issue.

VI. VENDOR RESPONSE

"It appears that the problem you have discovered was fixed in revision
1.96 of src/sys/i386/i386/sys_machdep.c on March 23, 2005, after being
found by the Coverity Prevent analysis tool; the commit message at the
time documented this as a local denial of service bug.

The policy of the FreeBSD Security Team is that local denial of service bugs
not be treated as security issues; it is possible that this problem will be
corrected in a future Erratum."

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2006-4172 to this issue. This is a candidate for inclusion in
the CVE list (http://cve.mitre.org), which standardizes names for 
security problems.

VIII. DISCLOSURE TIMELINE

08/16/2006  Initial vendor notification
08/16/2006  Initial vendor response
09/23/2006  Public disclosure

IX. CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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X. LEGAL NOTICES

Copyright =A9 2006 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.
There are no warranties with regard to this information. Neither the
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