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Fencer Intel
high 7.5

CVE-2026-81634 json

Possible heap buffer overflow during DNSSEC canonicalization

published last mo. modified last mo. also EUVD-2026-80290

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 41%
public exploits
0
none known

Summary

In NLnet Labs Unbound up to and including 1.26.0, a 255 length query name with a large TCP response can lead to a heap buffer overflow during the RRSet canonicalisation routine. This is caused by missing to add the first owner name into the buffer length check. A malicious actor operating a malicious name server or tampering with an incoming response to Unbound (canonicalisation happens before DNSSEC validation), can trigger the vulnerability.

Patch / fix

  • NLnet Labs Unbound 1.26.1
  • unbound Debian 13 1.26.1-0+deb13u1
  • unbound Debian 14 1.26.1-1

debian advisories DEBIAN-CVE-2026-81634

  • unbound Ubuntu 22.04 LTS 1.13.1-1ubuntu5.17
  • unbound Ubuntu 24.04 LTS 1.19.2-1ubuntu3.12
  • unbound Ubuntu 26.04 LTS 1.24.2-1ubuntu2.4
  • unbound Ubuntu Pro 14.04 LTS 1.4.22-1ubuntu4.14.04.3+esm5
  • unbound Ubuntu Pro 16.04 LTS 1.5.8-1ubuntu1.1+esm5
  • unbound Ubuntu Pro 18.04 LTS 1.6.7-1ubuntu2.6+esm6
  • unbound Ubuntu Pro 20.04 LTS 1.9.4-2ubuntu1.11+esm3

ubuntu advisories UBUNTU-CVE-2026-81634

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • unbound RHEL 9 1.24.2-3.el9_8.8
  • unbound-libs RHEL 9 1.24.2-3.el9_8.8
  • unbound-dracut RHEL 9 1.24.2-3.el9_8.8
  • python3-unbound RHEL 9 1.24.2-3.el9_8.8
  • unbound RHEL 10.2 1.24.2-7.el10_2.6
  • unbound-libs RHEL 10.2 1.24.2-7.el10_2.6
  • unbound-utils RHEL 10.2 1.24.2-7.el10_2.6
  • unbound-anchor RHEL 10.2 1.24.2-7.el10_2.6

red hat advisories RHSA-2026:71487RHSA-2026:71419RHSA-2026:70754RHSA-2026:68590

  • unbound Linux Micro 6.1 1.26.1-slfo.1.1_1.1
  • unbound SLES for SAP 15 SP5, SLES for SAP 15 SP4, SLES 15 SP5-LTSS +6 more 1.26.1-150100.10.31.1
  • unbound SLES for SAP 15 SP6, SLES 15 SP6-LTSS, SLE Module for Package Hub 15 SP7 +1 more 1.26.1-150600.23.24.1
  • unbound SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 1.26.1-160000.1.1
  • unbound Linux Micro 6.0 1.26.1-159998.1.1

suse advisories SUSE-SU-2026:24376-1SUSE-SU-2026:4624-1SUSE-SU-2026:4620-1SUSE-SU-2026:24128-1SUSE-SU-2026:24226-1SUSE-SU-2026:24135-1

  • unbound openSUSE Leap 16.0 1.26.1-160000.1.1
  • unbound openSUSE Tumbleweed 1.26.1-1.1

opensuse advisories openSUSE-SU-2026:22082-1openSUSE-SU-2026:11930-1

  • unbound AlmaLinux 10 1.24.2-7.el10_2.6
  • unbound-libs AlmaLinux 10 1.24.2-7.el10_2.6
  • unbound-utils AlmaLinux 10 1.24.2-7.el10_2.6
  • unbound-anchor AlmaLinux 10 1.24.2-7.el10_2.6
  • unbound-dracut AlmaLinux 10 1.24.2-7.el10_2.6
  • python3-unbound AlmaLinux 10 1.24.2-7.el10_2.6
  • unbound AlmaLinux 9 1.24.2-3.el9_8.8
  • unbound-libs AlmaLinux 9 1.24.2-3.el9_8.8

almalinux advisories ALSA-2026:71419ALSA-2026:71487ALSA-2026:70754

  • unbound Rocky Linux 9 1.24.2-3.el9_8.8
  • unbound Rocky Linux 10 1.24.2-7.el10_2.6
  • unbound Rocky Linux 8 1.16.2-5.14.el8_10.4

rocky linux advisories RLSA-2026:71487RLSA-2026:71419RLSA-2026:70754

  • unbound Azure Linux 3.0 1.26.1-1

azure linux advisories AZL-101721

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Is CVE-2026-81634 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-81634 updated cvss 7.5

unbound: Unbound: Heap buffer overflow via malicious DNSSEC response

  • Red Hat Enterprise Linux 6 unbound, unbound-libs, unbound-python
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 7 unbound, unbound-libs, unbound-python Red Hat OpenShift Container Platform 4 openshift/ose-rhel-coreos-8 Red Hat OpenShift Container Platform 5 openshift/ose-rhel-coreos-9
    affected: no fix available
  • Red Hat Enterprise Linux AppStream (v. 8) unbound 1.16.2-5.14.el8_10.4, unbound-libs 1.16.2-5.14.el8_10.4, python3-unbound 1.16.2-5.14.el8_10.4
    fixed: vendor fix RHSA-2026:70754
  • Red Hat Enterprise Linux AppStream (v. 9) unbound 1.24.2-3.el9_8.8, unbound-libs 1.24.2-3.el9_8.8, unbound-dracut 1.24.2-3.el9_8.8, python3-unbound 1.24.2-3.el9_8.8
    fixed: vendor fix RHSA-2026:71487
  • Red Hat Enterprise Linux AppStream (v. 10) unbound 1.24.2-7.el10_2.6, unbound-libs 1.24.2-7.el10_2.6, unbound-utils 1.24.2-7.el10_2.6, unbound-anchor 1.24.2-7.el10_2.6, unbound-dracut 1.24.2-7.el10_2.6, python3-unbound 1.24.2-7.el10_2.6
    fixed: vendor fix RHSA-2026:71419
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) unbound-devel 1.24.2-3.el9_8.8, unbound-debuginfo 1.24.2-3.el9_8.8, unbound-debugsource 1.24.2-3.el9_8.8, unbound-libs-debuginfo 1.24.2-3.el9_8.8, python3-unbound-debuginfo 1.24.2-3.el9_8.8
    fixed: vendor fix RHSA-2026:71487
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) unbound-devel 1.24.2-7.el10_2.6, unbound-debuginfo 1.24.2-7.el10_2.6, unbound-debugsource 1.24.2-7.el10_2.6, unbound-libs-debuginfo 1.24.2-7.el10_2.6, unbound-utils-debuginfo 1.24.2-7.el10_2.6, unbound-anchor-debuginfo 1.24.2-7.el10_2.6, +1 more
    fixed: vendor fix RHSA-2026:71419
  • Red Hat Hardened Images unbound 1.26.1-1.hum1, unbound-libs 1.26.1-1.hum1, unbound-munin 1.26.1-1.hum1, unbound-utils 1.26.1-1.hum1, unbound-anchor 1.26.1-1.hum1, unbound-dracut 1.26.1-1.hum1, +1 more
    fixed: vendor fix RHSA-2026:68590
show 1 more
  • Red Hat OpenShift Container Platform 4.22 rhcos 4.22.9.8.202609291947
    fixed: vendor fix RHSA-2026:74428

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
last mo.

Exploit prediction

0.48% chance of exploitation in the next 30 days, higher than 41% of all scored CVEs (FIRST EPSS, 2026-11-11).

CVSS scores

assigned by version score vector
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

  • NLnet Labs Unbound

Classification

Weakness
  • CWE-122 Heap-based Buffer Overflow

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.