CVE-2026-81642: Unbound DNSSEC validator buffer overflow with crafted DNSKEY (critical)

Critical 9.1 EPSS 1.0% Unbound

Unbound up to and including 1.26.0 can overflow its digest buffer while validating DNSSEC when a DNSKEY's owner name uses a compression pointer into its own RDATA. An attacker who controls a zone only needs to get a vulnerable resolver to query it, which can crash Unbound and possibly lead to remote code execution. NLnet Labs rates it Critical and Red Hat rates it Critical (CVSS 9.8). Debian 12 (bookworm) had no fixed package when this was written.

CVE-2026-81642CVE identifier
9.1CVSS 4.0 base score (critical)
1.0%EPSS: chance of exploitation in the next 30 days (higher than 62% of CVEs)
2026-09-16published

What do these terms mean? CVE · CVSS score · exploited (KEV) · EPSS · backported fix · all terms

What to do now

Check whether you run Unbound and which version (commands below).
Install the fixed version for your system: see “Patch it” below.
Restart the unbound service. Programs that link libunbound (for example DANE-aware mail servers) should also be restarted after the library update.
If you cannot patch today, apply the temporary mitigation below and patch as soon as possible.

Affected and fixed versions

Affected:

Unbound up to and including 1.26.0

Fixed in:

Unbound 1.26.1

Am I affected?

unbound -V | head -1
dpkg -l unbound libunbound8 | grep ^ii
rpm -q unbound unbound-libs

Patch it

Use the commands for your system. Distribution packages often keep an older version number with the fix backported, so compare with the fixed package versions in the table below, not only with the upstream version.

Debian

sudo apt update
sudo apt install --only-upgrade unbound libunbound8
sudo systemctl restart unbound

Ubuntu

sudo apt update
sudo apt install --only-upgrade unbound libunbound8
sudo systemctl restart unbound

RHEL, AlmaLinux, Rocky, Oracle

sudo dnf upgrade --refresh unbound unbound-libs
sudo systemctl restart unbound

Fedora

sudo dnf upgrade --refresh unbound unbound-libs

SUSE / openSUSE

sudo zypper refresh
sudo zypper update unbound libunbound8
sudo systemctl restart unbound

Amazon Linux

sudo dnf upgrade --releasever=latest unbound unbound-libs

Arch Linux

sudo pacman -Syu

Alpine

apk update && apk upgrade unbound unbound-libs

FreeBSD

pkg update && pkg upgrade unbound (port; base local-unbound is patched with freebsd-update)

Built from source

Install Unbound 1.26.1 from https://nlnetlabs.nl/downloads/unbound/unbound-1.26.1.tar.gz, or apply https://nlnetlabs.nl/downloads/unbound/patch_CVE-2026-81642.diff to 1.26.0 (patch -p1 < patch_CVE-2026-81642.diff; make install), then restart unbound.

General update steps for every system are on the Linux and Unix & BSD pages; after updating, see which services to restart.

Fix status in Linux distributions

Release	Package	Status	Fixed version / advisory
Debian 12	`unbound`	not fixed yet
Debian 13	`unbound`	fixed	`1.26.1-0+deb13u1`
Debian testing	`unbound`	fixed	`1.26.1-1`
Red Hat Enterprise Linux 9	`unbound-0:1.24.2-3.el9_8.8`	fixed	`RHSA-2026:71487`
Red Hat Enterprise Linux 8	`unbound-0:1.16.2-5.14.el8_10.4`	fixed	`RHSA-2026:70754`
Red Hat Enterprise Linux 6	`unbound`	out of support scope
Red Hat Enterprise Linux 10	`unbound-0:1.24.2-7.el10_2.6`	fixed	`RHSA-2026:71419`
Debian 13 (trixie)	`unbound`	fixed	`1.26.1-0+deb13u1 (DSA-6507-1)`
Ubuntu 26.04 LTS (resolute)	`unbound`	fixed	`1.24.2-1ubuntu2.3 (USN-8873-1)`
Ubuntu 24.04 LTS (noble)	`unbound`	fixed	`1.19.2-1ubuntu3.10 (USN-8873-1)`
Ubuntu 22.04 LTS (jammy)	`unbound`	fixed	`1.13.1-1ubuntu5.16 (USN-8873-1)`
RHEL 10	`unbound`	fixed	`1.24.2-7.el10_2.6 (RHSA-2026:71419)`
RHEL 9	`unbound`	fixed	`1.24.2-3.el9_8.8 (RHSA-2026:71487)`
RHEL 8	`unbound`	fixed	`1.16.2-5.14.el8_10.4 (RHSA-2026:70754)`
SUSE Linux Enterprise Server 16.0	`unbound`	fixed	`1.26.1-160000.1.1`
SUSE Linux Enterprise Server 15 SP7	`libunbound8`	fixed	`1.26.1-150600.23.24.1`

From the Debian security tracker, Ubuntu CVE tracker and Red Hat Security Data API, refreshed every few hours.

If you cannot patch yet

NLnet Labs offers only the patched release or the source patch; Red Hat states no mitigation meets its criteria.

Related vulnerabilities

Sources

Page generated automatically from official sources on 2026-11-03 18:05 UTC and reviewed by an editor. Always confirm with your vendor's advisory.