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============================================================================= FreeBSD-SA-26:36.ldns Security Advisory
The FreeBSD Project

Topic: Insufficient response validation in the ldns stub resolver

Category: contrib
Module: ldns
Announced: 2026-06-09
Credits: Pablo Ruiz from 'codecome.ai'
Affects: All supported versions of FreeBSD.
Corrected: 2026-06-09 19:17:37 UTC (stable/15, 15.1-STABLE)
2026-06-09 19:20:16 UTC (releng/15.1, 15.1-RC3-p1)
2026-06-09 19:19:55 UTC (releng/15.0, 15.0-RELEASE-p10)
2026-06-09 19:17:55 UTC (stable/14, 14.4-STABLE)
2026-06-09 19:19:17 UTC (releng/14.4, 14.4-RELEASE-p6)
2026-06-09 19:18:47 UTC (releng/14.3, 14.3-RELEASE-p15)
CVE Name: CVE-2026-10846

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

FreeBSD includes the ldns library from NLnet Labs, which provides DNS functionality for programs, including stub resolver support. Several
base system tools are built on ldns, among them drill(1), host(1), and
ssh(1) (for the VerifyHostKeyDNS feature).

II. Problem Description

When used as a stub resolver over UDP, ldns failed to verify that a
received response belonged to the outstanding query. It did not check
that the response source address and port matched the query
destination, that the transaction ID matched, or that the question
section of the response matched that of the query.

III. Impact

Without these checks, an off-path attacker who cannot observe the query
can forge UDP responses that ldns will accept as genuine. By injecting
spoofed replies, the attacker can return arbitrary DNS data to any
program that uses ldns for stub resolving, including drill(1).

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 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
# shutdown -r +10min "Rebooting for a security update"

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

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

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

3) 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-26:36/ldns.patch
# fetch https://security.FreeBSD.org/patches/SA-26:36/ldns.patch.asc
# gpg --verify ldns.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 all daemons that use the library, 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/ 20bfab98f8ae stable/15-n283890 releng/15.1/ 157d99d7ec9b releng/15.1-n283560 releng/15.0/ fbb19baa29ce releng/15.0-n281063 stable/14/ 5719a342555b stable/14-n274319 releng/14.4/ 410ab2bff36f releng/14.4-n273725 releng/14.3/ f61d7fc2ba85 releng/14.3-n271525
- -------------------------------------------------------------------------

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://www.cve.org/CVERecord?id=CVE-2026-10846>

The latest revision of this advisory is available at <URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-26:36.ldns.asc> -----BEGIN PGP SIGNATURE-----

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