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FreeBSD fails to limit number of TCP segments held in reassembly queue

Vulnerability Note VU#395670

Original Release Date: 2004-03-04 | Last Revised: 2004-03-04

Overview

FreeBSD fails to limit the number of TCP segments held in a reassembly queue which could allow an attacker to exhaust all available memory buffers (mbufs) on the destination system resulting in a denial-of-service condition.

Description

The Transmission Control Protocol (TCP) is part of the TCP/IP protocol suite and designed to provide reliable and connection-oriented service. In order to provide reliable service, TCP is designed to process packets that are delivered out of order so that these packets can later be re-assembled to create the entire TCP segment. There is a vulnerability in the way FreeBSD handles out-of-sequence TCP segments. When network packets making up a TCP segment are received out-of-sequence, these packets are held in a reassembly queue on the destination system so that they can be re-ordered and re-assembled. By sending a large number of out-of-sequence TCP packets, an unauthenticated, remote attacker could exhaust all memory buffers (mbufs) on the destination system resulting in a denial-of-service condition.

Impact

An unauthenticated, remote attacker could exhaust all memory buffers (mbufs) on the destination system resulting in a denial-of-service condition.

Solution

Upgrade

According to FreeBSD:

Upgrade to the FreeBSD stable branch (4-STABLE) or to the RELENG_5_2, RELENG_4_9, or RELENG_4_8 security branch dated after the correction date.

Apply Patch

According to FreeBSD:

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.asc

[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.asc

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.

Vendor Information

395670
Expand all

FreeBSD

Updated:  March 04, 2004

Status

  Vulnerable

Vendor Statement

No statement is currently available from the vendor regarding this vulnerability.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

Please refer to the FreeBSD Advisory.

If you have feedback, comments, or additional information about this vulnerability, please send us email.


CVSS Metrics

Group Score Vector
Base N/A N/A
Temporal N/A N/A
Environmental N/A

References

Credit

This vulnerability was reported by iDEFENSE

This document was written by Damon Morda.

Other Information

CVE IDs: CVE-2004-0171
Severity Metric: 6.83
Date Public: 2004-02-18
Date First Published: 2004-03-04
Date Last Updated: 2004-03-04 20:08 UTC
Document Revision: 26

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