FreeBSD Security Advisory FreeBSD-SA-20:04.tcp
19 March, 2020 by email@example.com | freebsd
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 ============================================================================= FreeBSD-SA-20:04.tcp Security Advisory The FreeBSD Project Topic: TCP IPv6 SYN cache kernel information disclosure Category: core Module: tcp Announced: 2020-03-19 Credits: Michael Tuexen (Netflix, contractor) Affects: All supported versions of FreeBSD. Corrected: 2020-03-08 14:48:21 UTC (stable/12, 12.1-STABLE) 2020-03-19 16:46:01 UTC (releng/12.1, 12.1-RELEASE-p3) 2020-03-08 14:48:32 UTC (stable/11, 11.3-STABLE) 2020-03-19 16:46:01 UTC (releng/11.3, 11.3-RELEASE-p7) CVE Name: CVE-2020-7451 For general information regarding FreeBSD Security Advisories, including descriptions of the fields above, security branches, and the following sections, please visit <URL:https://security.FreeBSD.org/>. I. Background The Internet Protocol version 6 (IPv6) header contains a one byte field called Traffic Class. Two bits of this field are used for Explicit Congestion Notification (ECN), the other six bits are used as Differentiated Services Field Codepoints (DSCP). The Transmission Control Protocol (TCP) is a connection oriented transport protocol, which can be used as an upper layer of IPv6. A TCP endpoint is either acting as a client (sending initially a SYN segment) or as a server (initially waiting to receive a SYN segment and then responding with a SYN-ACK segment). To mitigate the impact of some attacks against TCP servers (like SYN-flooding), FreeBSD uses specific code to handle the TCP connection setup for servers. This includes the transmission and retransmission of SYN-ACK segments or responding with a challenge ACK segment to a received RST segment. II. Problem Description When a TCP server transmits or retransmits a TCP SYN-ACK segment over IPv6, the Traffic Class field is not initialized. This also applies to challenge ACK segments, which are sent in response to received RST segments during the TCP connection setup phase. III. Impact For each TCP SYN-ACK (or challenge TCP-ACK) segment sent over IPv6, one byte of kernel memory is transmitted over the network. IV. Workaround No workaround is available. Systems not using IPv6 are unaffected. V. Solution Upgrade your vulnerable system to a supported FreeBSD stable or release / security branch (releng) dated after the correction date, and reboot. Perform one of the following: 1) To update your vulnerable system via a binary patch: Systems running a RELEASE version of FreeBSD on the i386 or amd64 platforms can be updated via the freebsd-update(8) utility: # freebsd-update fetch # freebsd-update install # shutdown -r +10min "Rebooting for a security update" 2) To update your vulnerable system via a source code patch: The following patches have been verified to apply to the applicable FreeBSD release branches. a) Download the relevant patch from the location below, and verify the detached PGP signature using your PGP utility. # fetch https://security.FreeBSD.org/patches/SA-20:04/tcp.patch # fetch https://security.FreeBSD.org/patches/SA-20:04/tcp.patch.asc # gpg --verify tcp.patch.asc b) Apply the patch. Execute the following commands as root: # cd /usr/src # patch < /path/to/patch c) Recompile your kernel as described in <URL:https://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the system. VI. Correction details The following list contains the correction revision numbers for each affected branch. Branch/path Revision - ------------------------------------------------------------------------- stable/12/ r358739 releng/12.1/ r359138 stable/11/ r358740 releng/11.3/ r359138 - ------------------------------------------------------------------------- To see which files were modified by a particular revision, run the following command, replacing NNNNNN with the revision number, on a machine with Subversion installed: # svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base Or visit the following URL, replacing NNNNNN with the revision number: <URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN> VII. References <URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-7451> The latest revision of this advisory is available at <URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-20:04.tcp.asc> -----BEGIN PGP SIGNATURE----- iQKTBAEBCgB9FiEE/A6HiuWv54gCjWNV05eS9J6n5cIFAl5zplhfFIAAAAAALgAo aXNzdWVyLWZwckBub3RhdGlvbnMub3BlbnBncC5maWZ0aGhvcnNlbWFuLm5ldEZD MEU4NzhBRTVBRkU3ODgwMjhENjM1NUQzOTc5MkY0OUVBN0U1QzIACgkQ05eS9J6n 5cLuzQ/9HvuKX5w2/CDerZPseNDKqumxjoap6MjfExvpVN4Auy31wcE7248JpZ/d I+Be927dmghiey97opVcR56g5OJ9QAinQRTWX1rLKaQ2xldGFE5924iLyQ/hjMXG LDkYrBpJ2Wkdq9XFZKAuu2dpV/RUMlGnKANG/QfAAd5V4VC7Sg5X6ty7ISlVMrM7 aQdBP4e5XyssfeqZeZ/A57dF3Yi7F1TEEjXeM+dulTET4nm0+w74n+QaNoH6hcMI n3Bb/SsF9HfbZtXz235vkzbgvvSX4f+D/d3vrcAA9KMVjKBH6QbiwJKuHSdb0GY8 ENMb7vO7Rx71u8GnCYg659qFrWb/kaTW2BCbgAJyp2747nAw8I7DwZiN2RKWA7qh JbcZb1rJN9gEccnGyNouuy4DzUlUc4VQnp4ajqV4S1YGbwdfsBqi2c0dYwqEcW96 RKxxTrH9JB8d52wMMshB7hMfwbeLeOJJ4phFL8knXuv19SWCP/tz6XDopoBN6wTW yn5g+n7oVCOsSwlPLHl/5WWUTvKjyCB6eZIblFhlbiNTuQiUaegDXx66On+vgVKD oYA9cDQUcvIKLne/KgCqTQ5MAuwE/7hPyUlGmuiZ3/Qx6CW568+v1kTc19eUQb0a +e5HDRFhtiQyRMpTC9Yt14sv8oFLynhyt/IbQWTeqppZhBugbJ8ÏKz -----END PGP SIGNATURE----- _______________________________________________ firstname.lastname@example.org mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-announce To unsubscribe, send any mail to "email@example.com"