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FreeBSD TCP PAWS Timestamp and TCP Options Bugs Let Remote Users Deny Service
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SecurityTracker Alert ID: 1014333
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SecurityTracker URL: http://securitytracker.com/id?1014333
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CVE Reference: CAN-2005-0356
, CAN-2005-2068
(Links to External Site)
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Date: Jun 29 2005
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Impact: Denial of service via network
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Fix Available: Yes
Vendor Confirmed: Yes
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Advisory: FreeBSD Security Advisory
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Version(s): 4.10, 4.11, 5.3, 5.4
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Description: Two vulnerabilities were reported in FreeBSD in the TCP stack implementation. A remote user can cause denial of service conditions.
The TCP Protection Against Wrapped Sequence Numbers (PAWS) timestamps option implementation allows a remote user to send a spoofed
packet with a large timer value to cause the target system to interpret subsequent packets asing being too old and, as a result,
discarding the packets [CVE: CAN-2005-0356]. A remote user can exploit this to cause TCP connections being processed by the target
system to be reset.
A remote user can also send a specially crafted TCP packet with the SYN flag set to overwrite certain TCP
options for established TCP connections [CVE: CAN-2005-2068].
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Impact: A remote user can cause denial of service conditions for existing TCP connections being processed by the target system.
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Solution: The vendor has issued a fix and has provided the following instructions [quoted].
Perform one of the following:
1) Upgrade
your vulnerable system to 4-STABLE or 5-STABLE, or to the RELENG_5_4, RELENG_5_3, RELENG_4_11, or RELENG_4_10 security branch dated
after the correction date.
2) To patch your present system:
The following patches have been verified to apply to FreeBSD 4.10,
4.11, 5.3, and 5.4 systems.
a) Download the relevant patch from the location below, and verify the detached PGP signature using
your PGP utility.
[FreeBSD 4.x]
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-05:15/tcp4.patch
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-
05:15/tcp4.patch.asc
[FreeBSD 5.x]
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-05:15/tcp.patch
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/S
A-05:15/tcp.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.
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Vendor URL: www.freebsd.org/ (Links to External Site)
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Cause: State error
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Underlying OS: UNIX (FreeBSD)
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Reported By: FreeBSD Security Advisories <security-advisories@freebsd.org>
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Message History:
None.
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Source Message Contents
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Date: Wed, 29 Jun 2005 21:55:05 GMT
From: FreeBSD Security Advisories <security-advisories@freebsd.org>
Subject: FreeBSD Security Advisory FreeBSD-SA-05:15.tcp
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-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
=============================================================================
FreeBSD-SA-05:15.tcp Security Advisory
The FreeBSD Project
Topic: TCP connection stall denial of service
Category: core
Module: inet
Announced: 2005-06-29
Credits: Noritoshi Demizu
Affects: All FreeBSD releases.
Corrected: 2005-06-29 21:38:48 UTC (RELENG_5, 5.4-STABLE)
2005-06-29 21:41:03 UTC (RELENG_5_4, 5.4-RELEASE-p3)
2005-06-29 21:42:33 UTC (RELENG_5_3, 5.3-RELEASE-p17)
2005-06-29 21:43:42 UTC (RELENG_4, 4.11-STABLE)
2005-06-29 21:45:14 UTC (RELENG_4_11, 4.11-RELEASE-p11)
2005-06-29 21:46:15 UTC (RELENG_4_10, 4.10-RELEASE-p16)
CVE Name: CAN-2005-0356, CAN-2005-2068
For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit
<URL:http://www.freebsd.org/security/>.
I. Background
The Transmission Control Protocol (TCP) of the TCP/IP protocol suite
provides a connection-oriented, reliable, sequence-preserving data
stream service. TCP timestamps are used to measure Round-Trip Time
and in the Protect Against Wrapped Sequences (PAWS) algorithm. TCP
packets with the SYN flag set are used during setup of new TCP
connections.
II. Problem Description
Two problems have been discovered in the FreeBSD TCP stack.
First, when a TCP packets containing a timestamp is received, inadequate
checking of sequence numbers is performed, allowing an attacker to
artificially increase the internal "recent" timestamp for a connection.
Second, a TCP packet with the SYN flag set is accepted for established
connections, allowing an attacker to overwrite certain TCP options.
III. Impact
Using either of the two problems an attacker with knowledge of the
local and remote IP and port numbers associated with a connection
can cause a denial of service situation by stalling the TCP connection.
The stalled TCP connection my be closed after some time by the other
host.
IV. Workaround
In some cases it may be possible to defend against these attacks by
blocking the attack packets using a firewall. Packets used to effect
either of these attacks would have spoofed source IP addresses.
V. Solution
Perform one of the following:
1) Upgrade your vulnerable system to 4-STABLE or 5-STABLE, or to the
RELENG_5_4, RELENG_5_3, RELENG_4_11, or RELENG_4_10 security branch
dated after the correction date.
2) To patch your present system:
The following patches have been verified to apply to FreeBSD 4.10,
4.11, 5.3, and 5.4 systems.
a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.
[FreeBSD 4.x]
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-05:15/tcp4.patch
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-05:15/tcp4.patch.asc
[FreeBSD 5.x]
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-05:15/tcp.patch
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-05:15/tcp.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.
VI. Correction details
The following list contains the revision numbers of each file that was
corrected in FreeBSD.
Branch Revision
Path
- -------------------------------------------------------------------------
RELENG_4
src/sys/netinet/tcp_input.c 1.107.2.44
RELENG_4_11
src/UPDATING 1.73.2.91.2.12
src/sys/conf/newvers.sh 1.44.2.39.2.15
src/sys/netinet/tcp_input.c 1.107.2.41.4.3
RELENG_4_10
src/UPDATING 1.73.2.90.2.17
src/sys/conf/newvers.sh 1.44.2.34.2.18
src/sys/netinet/tcp_input.c 1.107.2.41.2.1
RELENG_5
src/sys/netinet/tcp_input.c 1.252.2.16
RELENG_5_4
src/UPDATING 1.342.2.24.2.12
src/sys/conf/newvers.sh 1.62.2.18.2.8
src/sys/netinet/tcp_input.c 1.252.2.14.2.1
RELENG_5_3
src/UPDATING 1.342.2.13.2.20
src/sys/conf/newvers.sh 1.62.2.15.2.22
src/sys/netinet/tcp_input.c 1.252.4.1
- -------------------------------------------------------------------------
VII. References
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2005-0356
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2005-2068
http://www.kb.cert.org/vuls/id/637934
The latest revision of this advisory is available at
ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-05:15.tcp.asc
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.1 (FreeBSD)
iD8DBQFCwxe7FdaIBMps37IRAi39AJ9ss6PVEwloS4SlKEWi5S1hpHnzmACeJF7H
rKmK2NtleJ98dTLWW4QLMn4=
=6fBH
-----END PGP SIGNATURE-----
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