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Vulnerability Note VU#395670FreeBSD fails to limit number of TCP segments held in reassembly queueOverviewFreeBSD 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.I. DescriptionThe 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.II. ImpactAn unauthenticated, remote attacker could exhaust all memory buffers (mbufs) on the destination system resulting in a denial-of-service condition.III. SolutionUpgradeAccording 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:
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
References
This vulnerability was reported by iDEFENSE. This document was written by Damon Morda.
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