137 lines
5 KiB
Text
137 lines
5 KiB
Text
-----BEGIN PGP SIGNED MESSAGE-----
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Hash: SHA512
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=============================================================================
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FreeBSD-SA-17:06.openssh Security Advisory
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The FreeBSD Project
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Topic: OpenSSH Denial of Service vulnerability
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Category: contrib
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Module: OpenSSH
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Announced: 2017-08-10
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Affects: All supported versions of FreeBSD.
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Corrected: 2017-08-10 06:36:37 UTC (stable/11, 11.1-STABLE)
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2017-08-10 06:59:07 UTC (releng/11.1, 11.1-RELEASE-p1)
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2017-08-10 06:59:26 UTC (releng/11.0, 11.0-RELEASE-p12)
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2017-08-10 06:36:37 UTC (stable/10, 10.3-STABLE)
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2017-08-10 06:59:43 UTC (releng/10.3, 10.3-RELEASE-p21)
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CVE Name: CVE-2016-6515
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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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OpenSSH is an implementation of the SSH protocol suite, providing an
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encrypted and authenticated transport for a variety of services,
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including remote shell access.
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OpenSSH supports a built-in password authentication method, which is
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enabled with PasswordAuthentication. This option is disabled by
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default on FreeBSD.
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II. Problem Description
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There is no limit on the password length.
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III. Impact
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A remote attacker may be able to cause an affected SSH server to use
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excessive amount of CPU by sending very long passwords, when
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PasswordAuthentication is enabled by the system administrator.
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IV. Workaround
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Disable PasswordAuthentication in /etc/ssh/sshd_config and restart
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sshd. This is the default FreeBSD configuration.
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V. Solution
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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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Restart SSH service.
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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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Restart SSH service.
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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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# fetch https://security.FreeBSD.org/patches/SA-17:06/openssh.patch
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# fetch https://security.FreeBSD.org/patches/SA-17:06/openssh.patch.asc
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# gpg --verify openssh.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 the operating system using buildworld and installworld as
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described in <URL:https://www.FreeBSD.org/handbook/makeworld.html>.
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Restart the SSH daemon, or reboot the 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/ r322341
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releng/10.3/ r322344
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stable/11/ r322341
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releng/11.0/ r322343
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releng/11.1/ r322342
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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-2016-6515>
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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-17:06.openssh.asc>
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