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Posted on 16 February 2023
FreeBSD security notificat=============================================================================FreeBSD-SA-23:02.openssh Security Advisory
The FreeBSD Project
Topic: OpenSSH pre-authentication double free
Category: contrib
Module: openssh
Announced: 2023-02-16
Credits: Mantas Mikulenas
Affects: FreeBSD 12.4
Corrected: 2023-02-08 21:06:22 UTC (stable/13, 13.2-STABLE)
2023-02-08 21:07:30 UTC (stable/12, 12.4-STABLE)
2023-02-16 18:04:07 UTC (releng/12.4, 12.4-RELEASE-p2)
CVE Name: CVE-2023-25136
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
OpenSSH is an implementation of the SSH protocol suite, providing an
encrypted and authenticated transport for a variety of services,
including remote shell access.
II. Problem Description
A flaw in the backwards-compatibility key exchange route allows a pointer
to be freed twice.
III. Impact
A remote, unauthenticated attacker may be able to cause a denial of service,
or possibly remote code execution.
Note that FreeBSD 12.3 and FreeBSD 13.1 include older versions of OpenSSH,
and are not affected. FreeBSD 13.2-BETA1 and later include the fix.
IV. Workaround
No workaround is available.
V. Solution
Upgrade your vulnerable system to a supported FreeBSD stable or
release / security branch (releng) dated after the correction date.
Perform one of the following:
1) To update your vulnerable system via a binary patch:
Systems running a RELEASE version of FreeBSD on the amd64, i386, or
(on FreeBSD 13 and later) arm64 platforms can be updated via the
freebsd-update(8) utility:
# freebsd-update fetch
# freebsd-update install
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.
[FreeBSD 12.4]
# fetch https://security.FreeBSD.org/patches/SA-23:02/openssh.patch
# fetch https://security.FreeBSD.org/patches/SA-23:02/openssh.patch.asc
# gpg --verify openssh.patch.asc
b) Apply the patch. Execute the following commands as root:
# cd /usr/src
# patch < /path/to/patch
c) Recompile the operating system using buildworld and installworld as
described in <URL:https://www.FreeBSD.org/handbook/makeworld.html>.
Restart the applicable daemons, or reboot the system.
VI. Correction details
This issue is corrected by the corresponding Git commit hash or Subversion
revision number in the following stable and release branches:
Branch/path Hash Revision
- -------------------------------------------------------------------------
stable/13/ 296ec8eae0c8 stable/13-n260933
stable/12/ r372919
releng/12.4/ r372938
- -------------------------------------------------------------------------
For FreeBSD 13 and later:
Run the following command to see which files were modified by a
particular commit:
# git show --stat <commit hash>
Or visit the following URL, replacing NNNNNN with the hash:
<URL:https://cgit.freebsd.org/src/commit/?id=NNNNNN>
To determine the commit count in a working tree (for comparison against
nNNNNNN in the table above), run:
# git rev-list --count --first-parent HEAD
For FreeBSD 12 and earlier:
Run the following command to see which files were modified by a particular
revision, replacing NNNNNN with the revision number:
# 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-2023-25136>
The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-23:02.openssh.asc>
