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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> -----BEGIN PGP SIGNATURE-----

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