I. BACKGROUND
Free BSD is a free, Open Source unix operating system. More information
is available at http://www.freebsd.org/.
II. DESCRIPTION
Remote exploitation of a denial of service (DoS) vulnerability in
FreeBSD's memory buffers (mbufs) could allow attackers to launch a DoS
attack.
By sending many out-of-sequence packets, a low bandwidth denial of
service attack is possible against FreeBSD. When the targeted system
runs out of memory buffers (mbufs), it is no longer able to accept or
create new connections.
III. ANALYSIS
Exploitation of this vulnerability requires that the targeted system has
at least one open TCP port.
The DoS will last until the port is closed, either by the attacker or
the target machine.
iDEFENSE has proof of concept exploit code demonstrating the impact of
this vulnerability.
IV. DETECTION
iDEFENSE has confirmed that this vulnerability exists in FreeBSD 5.1
(default install from media). FreeBSD has stated that all versions are
affected.
V. WORKAROUND
"It may be possible to mitigate some denial-of-service attacks by
implementing timeouts at the application level."
VI. VENDOR RESPONSE
"Do one of the following:
1) Upgrade your vulnerable system to 4-STABLE, or to the RELENG_5_2,
RELENG_4_9, or RELENG_4_8 security branch dated after the correction
date.
OR
2) Patch your present system:
The following patch has been verified to apply to FreeBSD 4.x and 5.x
systems.
a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.
[FreeBSD 5.2] # fetch
ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-04:04/tcp52.patch # fetch
ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-04:04/tcp52.patch.as
c
[FreeBSD 4.8, 4.9] # fetch
ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-04:04/tcp47.patch # fetch
ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-04:04/tcp47.patch.as
c
b) Apply the patch.
# cd /usr/src # patch < /path/to/patch
c) Recompile your kernel as described in
<URL:http://www.freebsd.org/handbook/kernelconfig.html> and reboot the
system."
VII. CVE INFORMATION
The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CAN-2004-0171 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
| January 22, 2004 |
Exploit acquired by iDEFENSE |
| February 17, 2004 |
iDEFENSE clients notified |
| February 18, 2004 |
Initial vendor notification |
| February 18, 2004 |
Initial vendor response |
| March 02, 2004 |
Coordinated public disclosure |
IX. CREDIT
Alexander Cuttergo is credited with this discovery.
X. LEGAL NOTICES
Copyright © 2004 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
email 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.
