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FreeBSD-EN-26:11.dhclient                                       Errata Notice
                                                          The FreeBSD Project

Topic:          dhclient(8) lease validation is too strict

Category:       core
Module:         dhclient
Announced:      2026-05-01
Affects:        All supported versions of FreeBSD.
Corrected:      2026-04-30 21:07:00 UTC (stable/15, 15.0-STABLE)
                2026-05-01 15:08:46 UTC (releng/15.0, 15.0-RELEASE-p8)
                2026-04-30 21:07:11 UTC (stable/14, 14.4-STABLE)
                2026-05-01 15:08:37 UTC (releng/14.4, 14.4-RELEASE-p4)
                2026-05-01 15:08:30 UTC (releng/14.3, 14.3-RELEASE-p13)
                2026-04-30 21:07:24 UTC (stable/13, 13.5-STABLE)
                2026-05-01 15:08:19 UTC (releng/13.5, 13.5-RELEASE-p14)

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

Note: While FreeBSD 13.5 is end of life (EOL) as of May 1st, 2026, the
Security Team has decided to patch this issue as it was identified and a fix
was in-flight before the EOL date.

I.   Background

dhclient(8) is the default IPv4 DHCP client used on FreeBSD.  It is
responsible for contacting DHCP servers on a network segment and for
initialising and configuring network interfaces based on received
information.

When processing a DHCP offer, dhclient passes various parameters provided by
the server to dhclient-script(8).  DHCP options, as documented in
dhcp-options(5), are passed via the environment.

II.  Problem Description

The patch for FreeBSD-SA-26:15.dhclient introduced some validation of the
boot file DHCP option to prevent unescaped values from being written to the
stored lease file.  This validation is overly strict and rejects Windows
paths.

III. Impact

The overly strict validation may cause dhclient(8) to reject valid leases.

IV.  Workaround

No workaround is available.  Systems not running dhclient(8) are not
affected.

V.   Solution

Upgrade your 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 system installed from base system packages:

Systems running a 15.0-RELEASE version of FreeBSD on the amd64 or arm64
platforms, which were installed using base system packages, can be updated
via the pkg(8) utility:

# pkg upgrade -r FreeBSD-base

2) To update your system installed from binary distribution sets:

Systems running a RELEASE version of FreeBSD on the amd64 or arm64 platforms,
or the i386 platform on FreeBSD 13, which were not installed using base
system packages, can be updated via the freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install

3) To update your 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/EN-26:11/dhclient.patch
# fetch https://security.FreeBSD.org/patches/EN-26:11/dhclient.patch.asc
# gpg --verify dhclient.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 as of the corresponding Git commit hash in the
following stable and release branches:

Branch/path                             Hash                     Revision
- -------------------------------------------------------------------------
stable/15/                              252f603d1704    stable/15-n283453
releng/15.0/                            dc8762cfb6e2  releng/15.0-n281035
stable/14/                              2f9478ad42c4    stable/14-n274094
releng/14.4/                            dfcb69cdb07e  releng/14.4-n273699
releng/14.3/                            5bad905eb37f  releng/14.3-n271499
stable/13/                              b1ece85741db    stable/13-n259871
releng/13.5/                            b362b6b6c8f2  releng/13.5-n259221
- -------------------------------------------------------------------------

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

VII. References

<URL:https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=294886>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-26:11.dhclient.asc>
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