FreeBSD Security Advisories
2005-Jun-29 21:55 UTC
FreeBSD Security Advisory FreeBSD-SA-05:15.tcp
-----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-----