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FreeBSD-SA-20:03.thrmisc Security Advisory
The FreeBSD Project

Topic: kernel stack data disclosure

Category: core
Module: kernel
Announced: 2020-01-28
Credits: Ilja Van Sprundel
Affects: All supported versions of FreeBSD.
Corrected: 2019-11-15 16:40:10 UTC (stable/12, 12.1-STABLE)
2020-01-28 18:57:45 UTC (releng/12.1, 12.1-RELEASE-p2)
2020-01-28 18:57:45 UTC (releng/12.0, 12.0-RELEASE-p13)
2019-11-15 16:40:55 UTC (stable/11, 11.3-STABLE)
2020-01-28 18:57:45 UTC (releng/11.3, 11.3-RELEASE-p6)
CVE Name: CVE-2019-15875

For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:https://security.FreeBSD.org/>.

I. Background

The kernel can create a core dump file when a process crashes that contains
process state, for debugging.

II. Problem Description

Due to incorrect initialization of a stack data structure, up to 20 bytes of
kernel data stored previously stored on the stack will be exposed to a
crashing user process.

III. Impact

Sensitive kernel data may be disclosed.

IV. Workaround

Core dumps may be disabled by setting the kern.coredump sysctl to 0.
See sysctl(8) and sysctl.conf(5).

V. Solution

Upgrade your vulnerable system to a supported FreeBSD stable or
release / security branch (releng) dated after the correction date,
and reboot.

Perform one of the following:

1) To update your vulnerable system via a binary patch:

Systems running a RELEASE version of FreeBSD on the i386 or amd64
platforms can be updated via the freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install
# shutdown -r +10min “Rebooting for a security update”

2) To update your vulnerable system via a source code patch:

The following patches have been verified to apply to the applicable
FreeBSD release branches.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

# fetch https://security.FreeBSD.org/patches/SA-20:03/thrmisc.patch
# fetch https://security.FreeBSD.org/patches/SA-20:03/thrmisc.patch.asc
# gpg –verify thrmisc.patch.asc

b) Apply the patch. Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch

c) Recompile your kernel as described in
<URL:https://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.

VI. Correction details

The following list contains the correction revision numbers for each
affected branch.

Branch/path Revision
– ————————————————————————-
stable/12/ r354734
releng/12.1/ r357219
releng/12.0/ r357219
stable/11/ r354735
releng/11.3/ r357219
– ————————————————————————-

To see which files were modified by a particular revision, run the
following command, replacing NNNNNN with the revision number, on a
machine with Subversion installed:

# svn diff -cNNNNNN –summarize svn://svn.freebsd.org/base

Or visit the following URL, replacing NNNNNN with the revision number:

<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-15875>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-20:03.thrmisc.asc>
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