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iDefense Security Advisory 10.10.06: FreeBSD ptrace PT_LWPINFO Denial of Service Vulnerability
From: iDefense Labs <labs-no-reply () idefense com>
Date: Thu, 12 Oct 2006 13:16:37 -0400

FreeBSD ptrace PT_LWPINFO Denial of Service Vulnerability

iDefense Security Advisory 10.10.06
Oct 10, 2006


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

The PT_LWPINFO ptrace command allows a tracer to get information on a
running thread.


Local exploitation of a design error in version 6 of The FreeBSD
Project's FreeBSD operating system allows attackers to create a denial
of service (DoS) condition.

The problem specifically exists due to the kern_ptrace function
returning without properly releasing locks. Consider the following code

953         case PT_LWPINFO:
954                 if (data == 0 || data > sizeof(*pl))
955                         return (EINVAL);

If the "data" variable is out of range, the function will return without
releasing locks. When the next signal or process operation dealing with
this process occurs, the machine will lock up.

Additionally, the "addr" variable is not properly checked for validity.
When an unmapped user-space address is supplied, the kernel will panic.
This is due to the invalid memory address being passed to "copyout" as
seen below.

450         case PT_LWPINFO:
451                 error = copyout(&r.pl, uap->addr, uap->data);
452                 break;
453         }


Exploitation of this vulnerability would result in a DoS condition on
the affected host. In the case of an invalid length value, exploitation
will result in a hard lock up. In the case of a valid length with an
invalid user-space memory address, exploitation will result in a kernel
panic leading to reboot.


iDefense has confirmed the existence of this problem in FreeBSD version
6.0-RELEASE. FreeBSD 6.1-RELEASE is not affected. It is suspected that
other versions are also affected.


iDefense is not aware of any workaround for this issue.


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

The locking issue was addressed with revision of sys_process.c
from the FreeBSD kernel source. The kernel panic issue was addressed
with revision 1.136 of sys_process.c. These revisions are available via


The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2006-4516 to this issue. This is a candidate for inclusion in
the CVE list (http://cve.mitre.org), which standardizes names for
security problems.


08/18/2006  Initial vendor notification
10/06/2006  Initial vendor response
10/10/2006  Public disclosure
10/12/2005  Revised public disclosure


The discoverer of this vulnerability wishes to remain anonymous.

Thanks go to Ilja van Sprundel for helping to with the analysis of this

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Copyright © 2006 iDefense, Inc.

Permission is granted for the redistribution of this alert
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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
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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