Vulnerability Note VU#395670

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

Original Release date: 04 Mar 2004 | Last revised: 04 Mar 2004

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.

Systems Affected (Learn More)

VendorStatusDate NotifiedDate Updated
FreeBSDAffected-04 Mar 2004
If you are a vendor and your product is affected, let us know.

CVSS Metrics (Learn More)

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

References

Credit

This vulnerability was reported by iDEFENSE .

This document was written by Damon Morda.

Other Information

  • CVE IDs: CAN-2004-0171
  • Date Public: 18 Feb 2004
  • Date First Published: 04 Mar 2004
  • Date Last Updated: 04 Mar 2004
  • Severity Metric: 6.83
  • Document Revision: 26

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