161 lines
6.2 KiB
Text
161 lines
6.2 KiB
Text
-----BEGIN PGP SIGNED MESSAGE-----
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Hash: SHA512
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=============================================================================
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FreeBSD-SA-15:22.openssh Security Advisory
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The FreeBSD Project
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Topic: OpenSSH multiple vulnerabilities
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Category: contrib
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Module: openssh
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Announced: 2015-08-25
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Affects: All supported versions of FreeBSD.
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Corrected: 2015-08-25 20:48:44 UTC (stable/10, 10.2-STABLE)
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2015-08-25 20:48:51 UTC (releng/10.2, 10.2-RC3-p2)
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2015-08-25 20:48:51 UTC (releng/10.2, 10.2-RELEASE-p2)
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2015-08-25 20:48:58 UTC (releng/10.1, 10.1-RELEASE-p19)
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2015-08-25 20:48:44 UTC (stable/9, 9.3-STABLE)
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2015-08-25 20:49:05 UTC (releng/9.3, 9.3-RELEASE-p24)
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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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The PAM (Pluggable Authentication Modules) library provides a flexible
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framework for user authentication and session setup / teardown.
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The default FreeBSD OpenSSH configuration has PAM interactive
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authentication enabled.
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Privilege separation is a technique in which a program is divided into
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multiple cooperating processes, each with a different task, where each
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process is limited to the specific privileges required to perform that
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specific task, while the privileged parent process acts as an arbiter.
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II. Problem Description
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A programming error in the privileged monitor process of the sshd(8)
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service may allow the username of an already-authenticated user to be
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overwritten by the unprivileged child process.
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A use-after-free error in the privileged monitor process of he sshd(8)
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service may be deterministically triggered by the actions of a
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compromised unprivileged child process.
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A use-after-free error in the session multiplexing code in the sshd(8)
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service may result in unintended termination of the connection.
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III. Impact
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The first bug may allow a remote attacker who a) has already succeeded
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by other means in compromising the unprivileged pre-authentication
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child process and b) has valid credentials to one user on the target
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system to impersonate a different user.
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The second bug may allow a remote attacker who has already succeeded
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by other means in compromising the unprivileged pre-authentication
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child process to bypass PAM authentication entirely.
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The third bug is not exploitable, but can cause premature termination
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of a multiplexed ssh connection.
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IV. Workaround
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No workaround is available, but systems where ssh(1) and sshd(8) are
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not used are not vulnerable.
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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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The sshd(8) service has to be restarted after the update. A reboot
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is recommended but not required.
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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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The sshd(8) service has to be restarted after the update. A reboot
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is recommended but not required.
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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-15:22/openssh.patch
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# fetch https://security.FreeBSD.org/patches/SA-15:22/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 sshd(8) 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/9/ r287144
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releng/9.3/ r287147
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stable/10/ r287144
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releng/10.1/ r287146
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releng/10.2/ r287145
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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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The latest revision of this advisory is available at
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<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-15:22.openssh.asc>
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