128 lines
4.8 KiB
Text
128 lines
4.8 KiB
Text
-----BEGIN PGP SIGNED MESSAGE-----
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Hash: SHA512
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=============================================================================
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FreeBSD-SA-16:21.43bsd Security Advisory
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The FreeBSD Project
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Topic: Kernel stack disclosure in 4.3BSD compatibility layer
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Category: core
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Module: kernel
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Announced: 2016-05-31
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Credits: CTurt
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Affects: All supported versions of FreeBSD.
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Corrected: 2016-05-31 16:57:42 UTC (stable/10, 10.3-STABLE)
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2016-05-31 16:55:50 UTC (releng/10.3, 10.3-RELEASE-p4)
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2016-05-31 16:55:45 UTC (releng/10.2, 10.2-RELEASE-p18)
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2016-05-31 16:55:41 UTC (releng/10.1, 10.1-RELEASE-p35)
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2016-05-31 16:58:00 UTC (stable/9, 9.3-STABLE)
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2016-05-31 16:55:37 UTC (releng/9.3, 9.3-RELEASE-p43)
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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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FreeBSD has binary compatibility layer with historic 4.3BSD operating
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system.
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II. Problem Description
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The implementation of historic stat(2) system call does not clear the
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output struct before copying it out to userland.
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III. Impact
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An unprivileged user can read a portion of uninitialised kernel stack data,
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which may contain sensitive information, such as the stack guard, portions
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of the file cache or terminal buffers, which an attacker might leverage to
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obtain elevated privileges.
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IV. Workaround
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No workaround is available, but systems not using the 4.3BSD compatibility
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layer are not vulnerable.
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The 4.3BSD compatibility layer is not included into the default GENERIC kernel
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configuration. A custom kernel config that does not have the COMPAT_43 option
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is also 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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Reboot is required.
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2) 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-16:21/stat.patch
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# fetch https://security.FreeBSD.org/patches/SA-16:21/stat.patch.asc
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# gpg --verify stat.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/9/ r301055
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releng/9.3/ r301049
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stable/10/ r301054
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releng/10.1/ r301050
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releng/10.2/ r301051
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releng/10.3/ r301052
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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:http://cturt.github.io/compat-info-leaks.html>
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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-16:21.43bsd.asc>
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