FreeBSD Security Advisory FreeBSD-SA-18:08.tcp
6 August, 2018 by email@example.com | 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 <firstname.lastname@example.org> 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) 2018-08-06 17:47:47 UTC (releng/11.2, 11.2-RELEASE-p1) 2018-08-06 17:48:46 UTC (releng/11.1, 11.1-RELEASE-p12) 2018-08-06 18:47:03 UTC (stable/10, 10.4-STABLE) 2018-08-06 17:50:40 UTC (releng/10.4, 10.4-RELEASE-p10) 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/>. 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 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/ r337389 stable/11/ r337391 releng/11.1/ r337388 releng/11.2/ r337387 - ------------------------------------------------------------------------- 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/A6HiuWv54gCjWNV05eS9J6n5cIFAltosd4ACgkQ05eS9J6n 5cKLRRAApitUTx46nToGtbCr/fzEZtYpjU0L/kMDwFw8ngfrb3MR4yht087t8JK1 jZlbeKRQwYjN+ecLrO3QdWoM4LavQK/cYuWq2tCpJiwqXK15rDJGBJjlBiAsmupF fGGSD2DcJ/Jz7zTKDkjybCh83QGGTt/HBZRYLc85ipJPHgPQQtnD/OLjFK34Lr45 vEss9AAkBEe4ZWiSltrQYzqMYf8+sCz/OYP+NGluz4eUjuzKogqyLIAA29auqoNp UY5tIUhf8dcB9oeARxWlvmxTKSLB5kevF5jsBzxB8Ap1xUfLFip02h6ApL0xuWz2 ouX/gN8KBgmJoNIP+GbBY29sQCEY0GTIR9q/dO1ZB3CePJFQsvWjtNeBBjIK66On xJSSrUXDPANfcePbnCN9JdsclSEJ0+EBYol3hSWVY8bX3OMcOZw1wRXXCwN0T3of QQwbuP0ORt5OdsOObwaxDJEWLEma7N2swWF5YR0oQl0+ETvkIsqFilsTlY6qEB/L WG9G1Y9uVn++AJs7HzI+vKVEhhwtJep+7ks28sH5J0LQiUGYfwRACYfVLgi6iXNV YKPB4hUFd2d8QaYWdgU92YBJWrR8bqyDdetifMEG5tP+TFCeNCh6SMpRnL7Lzns+ hkZiRHJeIT7tGu77xZknFI6ghDHOdemtZ/QiL0NsrM05spWkdIA= =HNsD -----END PGP SIGNATURE----- _______________________________________________ email@example.com mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-announce To unsubscribe, send any mail to "firstname.lastname@example.org"