168 lines
6.4 KiB
Text
168 lines
6.4 KiB
Text
-----BEGIN PGP SIGNED MESSAGE-----
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Hash: SHA512
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=============================================================================
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FreeBSD-SA-18:08.tcp Security Advisory
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The FreeBSD Project
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Topic: Resource exhaustion in TCP reassembly
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Category: core
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Module: inet
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Announced: 2018-08-06
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Credits: Juha-Matti Tilli <juha-matti.tilli@iki.fi> from
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Aalto University, Department of Communications and Networking
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and Nokia Bell Labs
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Affects: All supported versions of FreeBSD.
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Corrected: 2018-08-06 18:46:09 UTC (stable/11, 11.1-STABLE)
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2018-08-06 17:47:47 UTC (releng/11.2, 11.2-RELEASE-p1)
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2018-08-06 17:48:46 UTC (releng/11.1, 11.1-RELEASE-p12)
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2018-08-06 18:47:03 UTC (stable/10, 10.4-STABLE)
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2018-08-06 17:50:40 UTC (releng/10.4, 10.4-RELEASE-p10)
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CVE Name: CVE-2018-6922
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For general information regarding FreeBSD Security Advisories,
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including descriptions of the fields above, security branches, and the
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following sections, please visit <URL:https://security.FreeBSD.org/>.
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I. Background
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The Transmission Control Protocol (TCP) of the TCP/IP protocol suite
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provides a connection-oriented, reliable, sequence-preserving data
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stream service.
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To transmit a stream of data, TCP breaks the data stream into segments
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for transmission through the Internet, and reassembles the segments at
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the receiving side to recreate the data stream.
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II. Problem Description
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One of the data structures that holds TCP segments uses an inefficient
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algorithm to reassemble the data. This causes the CPU time spent on
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segment processing to grow linearly with the number of segments in the
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reassembly queue.
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III. Impact
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An attacker who has the ability to send TCP traffic to a victim system
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can degrade the victim system's network performance and/or consume
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excessive CPU by exploiting the inefficiency of TCP reassembly
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handling, with relatively small bandwidth cost.
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IV. Workaround
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As a workaround, system administrators should configure their systems
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to only accept TCP connections from trusted end-stations, if it is
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possible to do so.
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For systems which must accept TCP connections from untrusted
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end-stations, the workaround is to limit the size of each reassembly
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queue. The capability to do that is added by the patches noted in the
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"Solution" section below.
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V. Solution
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As a temporary solution to this problem, these patches limit the size
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of each TCP connection's reassembly queue. The value is controlled by
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a sysctl (net.inet.tcp.reass.maxqueuelen), which sets the maximum
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number of TCP segments that can be outstanding on a session's
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reassembly queue. This value defaults to 100.
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Note that setting this value too low could impact the throughput of
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TCP connections which experience significant loss or
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reordering. However, the higher this number is set, the more resources
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can be consumed on TCP reassembly processing.
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Perform one of the following:
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1) Upgrade your vulnerable system to a supported FreeBSD stable or
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release / security branch (releng) dated after the correction date.
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Afterward, reboot the system.
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2) To update your vulnerable system via a binary patch:
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Systems running a RELEASE version of FreeBSD on the i386 or amd64
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platforms can be updated via the freebsd-update(8) utility:
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# freebsd-update fetch
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# freebsd-update install
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Afterward, reboot the system.
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3) To update your vulnerable system via a source code patch:
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The following patches have been verified to apply to the applicable
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FreeBSD release branches.
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a) Download the relevant patch from the location below, and verify the
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detached PGP signature using your PGP utility.
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[FreeBSD 10.4]
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# fetch https://security.FreeBSD.org/patches/SA-18:08/tcp-10.patch
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# fetch https://security.FreeBSD.org/patches/SA-18:08/tcp-10.patch.asc
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# gpg --verify tcp-10.patch.asc
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[FreeBSD 11.x]
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# fetch https://security.FreeBSD.org/patches/SA-18:08/tcp-11.patch
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# fetch https://security.FreeBSD.org/patches/SA-18:08/tcp-11.patch.asc
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# gpg --verify tcp-11.patch.asc
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b) Apply the patch. Execute the following commands as root:
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# cd /usr/src
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# patch < /path/to/patch
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c) Recompile your kernel as described in
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<URL:https://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
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system.
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VI. Correction details
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The following list contains the correction revision numbers for each
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affected branch.
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Branch/path Revision
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- -------------------------------------------------------------------------
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stable/10/ r337392
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releng/10.4/ r337389
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stable/11/ r337391
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releng/11.1/ r337388
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releng/11.2/ r337387
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- -------------------------------------------------------------------------
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To see which files were modified by a particular revision, run the
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following command, replacing NNNNNN with the revision number, on a
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machine with Subversion installed:
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# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base
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Or visit the following URL, replacing NNNNNN with the revision number:
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<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>
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VII. References
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<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-6922>
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<URL:https://www.kb.cert.org/vuls/id/962459>
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The latest revision of this advisory is available at
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<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-18:08.tcp.asc>
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