140 lines
5.5 KiB
Text
140 lines
5.5 KiB
Text
-----BEGIN PGP SIGNED MESSAGE-----
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Hash: SHA512
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=============================================================================
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FreeBSD-SA-18:04.vt Security Advisory
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The FreeBSD Project
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Topic: vt console memory disclosure
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Category: core
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Module: vt console
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Announced: 2018-04-04
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Credits: Dr Silvio Cesare of InfoSect
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Affects: All supported versions of FreeBSD.
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Corrected: 2018-04-04 05:24:59 UTC (stable/11, 11.1-STABLE)
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2018-04-04 05:33:56 UTC (releng/11.1, 11.1-RELEASE-p9)
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2018-04-04 05:26:33 UTC (stable/10, 10.4-STABLE)
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2018-04-04 05:33:56 UTC (releng/10.4, 10.4-RELEASE-p8)
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2018-04-04 05:33:56 UTC (releng/10.3, 10.3-RELEASE-p29)
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CVE Name: CVE-2018-6917
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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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On FreeBSD 11 and later, and FreeBSD 10.x systems that boot via UEFI, the
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default system video console is provided by the vt(4) driver. The console
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allows the user, including an unprivileged user, to load a font at runtime.
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II. Problem Description
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Insufficient validation of user-provided font parameters can result in an
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integer overflow, leading to the use of arbitrary kernel memory as glyph
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data. Characters that reference this data can be displayed on the screen,
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effectively disclosing kernel memory.
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III. Impact
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Unprivileged users may be able to access privileged kernel data.
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Such memory might contain sensitive information, such as portions of the file
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cache or terminal buffers. This information might be directly useful, or it
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might be leveraged to obtain elevated privileges in some way; for example,
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a terminal buffer might include a user-entered password.
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IV. Workaround
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The syscons sc(4) system console is not affected by this issue and may be
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used on systems that do not boot via UEFI. To use the syscons console,
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set the kern.vty tunable in /boot/loader.conf as described in sc(4), and
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reboot. No workaround is available for systems that boot via UEFI.
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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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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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A reboot is required after the upgrade.
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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-18:04/vt.patch
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# fetch https://security.FreeBSD.org/patches/SA-18:04/vt.patch.asc
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# gpg --verify vt.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/ r331983
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releng/10.3/ r331984
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releng/10.4/ r331984
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stable/11/ r331982
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releng/11.1/ r331984
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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-2018-6917>
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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-18:04.vt.asc>
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