FreeBSD Security Advisory FreeBSD-SA-18:08.tcp
15 August, 2018 by firstname.lastname@example.org | freebsd
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 ============================================================================= FreeBSD-SA-18:08.tcp Security Advisory The FreeBSD Project Topic: Resource exhaustion in TCP reassembly Category: core Module: inet Announced: 2018-08-06 Credits: Juha-Matti Tilli <email@example.com> from Aalto University, Department of Communications and Networking and Nokia Bell Labs Affects: All supported versions of FreeBSD. Corrected: 2018-08-06 18:46:09 UTC (stable/11, 11.1-STABLE) 2018-08-15 02:30:11 UTC (releng/11.2, 11.2-RELEASE-p2) 2018-08-15 02:30:11 UTC (releng/11.1, 11.1-RELEASE-p13) 2018-08-06 18:47:03 UTC (stable/10, 10.4-STABLE) 2018-08-15 02:31:10 UTC (releng/10.4, 10.4-RELEASE-p11) CVE Name: CVE-2018-6922 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/>. 0. Revision history v1.0 2018-08-06 Initial release. v1.1 2018-08-14 Fixed documentation date in manual pages. I. Background The Transmission Control Protocol (TCP) of the TCP/IP protocol suite provides a connection-oriented, reliable, sequence-preserving data stream service. To transmit a stream of data, TCP breaks the data stream into segments for transmission through the Internet, and reassembles the segments at the receiving side to recreate the data stream. II. Problem Description One of the data structures that holds TCP segments uses an inefficient algorithm to reassemble the data. This causes the CPU time spent on segment processing to grow linearly with the number of segments in the reassembly queue. III. Impact An attacker who has the ability to send TCP traffic to a victim system can degrade the victim system's network performance and/or consume excessive CPU by exploiting the inefficiency of TCP reassembly handling, with relatively small bandwidth cost. IV. Workaround As a workaround, system administrators should configure their systems to only accept TCP connections from trusted end-stations, if it is possible to do so. For systems which must accept TCP connections from untrusted end-stations, the workaround is to limit the size of each reassembly queue. The capability to do that is added by the patches noted in the "Solution" section below. V. Solution As a temporary solution to this problem, these patches limit the size of each TCP connection's reassembly queue. The value is controlled by a sysctl (net.inet.tcp.reass.maxqueuelen), which sets the maximum number of TCP segments that can be outstanding on a session's reassembly queue. This value defaults to 100. Note that setting this value too low could impact the throughput of TCP connections which experience significant loss or reordering. However, the higher this number is set, the more resources can be consumed on TCP reassembly processing. Perform one of the following: 1) Upgrade your vulnerable system to a supported FreeBSD stable or release / security branch (releng) dated after the correction date. Afterward, reboot the system. 2) 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 Afterward, reboot the system. 3) 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. [FreeBSD 10.4] # fetch https://security.FreeBSD.org/patches/SA-18:08/tcp-10.patch # fetch https://security.FreeBSD.org/patches/SA-18:08/tcp-10.patch.asc # gpg --verify tcp-10.patch.asc [FreeBSD 11.x] # fetch https://security.FreeBSD.org/patches/SA-18:08/tcp-11.patch # fetch https://security.FreeBSD.org/patches/SA-18:08/tcp-11.patch.asc # gpg --verify tcp-11.patch.asc [*** v1.1 NOTE ***] Patchsets are provided for completeness, it have little impact to runtime behavior. [FreeBSD 10.4] # fetch https://security.FreeBSD.org/patches/SA-18:08/tcp-man-10.patch # fetch https://security.FreeBSD.org/patches/SA-18:08/tcp-man-10.patch.asc # gpg --verify tcp-man-10.patch.asc [FreeBSD 11.x] # fetch https://security.FreeBSD.org/patches/SA-18:08/tcp-man-11.patch # fetch https://security.FreeBSD.org/patches/SA-18:08/tcp-man-11.patch.asc # gpg --verify tcp-man-11.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/10/ r337392 releng/10.4/ r337832 stable/11/ r337391 releng/11.1/ r337828 releng/11.2/ r337828 - ------------------------------------------------------------------------- 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-2018-6922> <URL:https://www.kb.cert.org/vuls/id/962459> The latest revision of this advisory is available at <URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-18:08.tcp.asc> -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.2.9 (FreeBSD) iQIzBAEBCgAdFiEE/A6HiuWv54gCjWNV05eS9J6n5cIFAltztakACgkQ05eS9J6n 5cLN1A//XMCorSih94rs9zvkRPj8g3eN4es5QD9QzI9IwLlfK8DTvtMM9XUKsNT2 vxgJK8Mnl6N5NddRyiV8o0CioRQF+cmN4cnMhf0LRN6Rv0PqWpsbuuRdWgVtm/aV yHNEvnY32RbaZ6YQWmAhG9b+7JztWCpv2MawIaIdy6QFWmHV50ElDj5k1QBHauDd 2+P3u3+ohbXNMAZGQjIMQwxIgU7BRTVKASa/GzkPSCwQHFabbtm7aL/jEhzySfdl bA6ZsMPhr0QqLORKqt8kAUzzFgpVdSRLCa+a8H9phi3CqPDEzGCDdseiCw4mJ+VU EhFu616EKw7V9G7FXpnK3Z+E0aHe6UYlf4swUzXluWJrtO/n5bD++ObZaSUOPH0l arcOUe8S5dnHiZ8Gg9BqtT6nKQMPXHgGh8W3U53CPt0USJsUWMPd0GPVYt2QnbkX 27leNs7e1+Njes4PuhOJ+wunn1iye+eTVilqaGkuFC+YKiOJVs9pNJovBTalTsfB XqQO52DesrJ/C0xo3AaaNGfNB4JhG3rqR2tPiqubNQcEIocTJ7LkGy0lKXiDbIra UA7fDszAG5l5RSyRtgQ4QPd+EzvYguX1vccFGqItDX9aZdQDspnnViKl/FJNzb19 p9fEa+ZVjV65N836RhCtRx7allqhTAX4yQFXIrUiwQ3ssLNAx1s= =sl/Z -----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"