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CVE-2026-81634

HIGH 7.5

Published 2026-09-16 · Last modified 2026-09-16

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.

ELEVATED IMPACT

Severe if exploited (CVSS 7.5), but no known exploitation and low modeled probability. Patch on a normal cadence.

Exploitation likelihood

0.5%chance of exploitation in 30 days · 41st percentile

○ In CISA KEV ○ Catalogued PoC

Impact if exploited

7.5CVSS 3.1 · HIGH

  • ConfidentialityNone
  • IntegrityNone
  • AvailabilityHigh

What an attacker needs

  • ✓Access: Reachable over the network — no local access needed
  • ✓Privileges: No account or privileges required
  • ✓User interaction: No user interaction needed
  • ✓Complexity: No special conditions — reliably repeatable

✓ lowers the bar for an attacker · ⚠ raises it

Proof of concept

No public PoC is currently catalogued.

Search for new PoCs

Search GitHub now — results may be empty or unverified.

Tracked sources are checked daily for recent CVEs, including PoCs published after the original disclosure. A later release appears after a tracked source lists it and a refresh succeeds.

Data snapshot:

Affected

Vendors Nlnet Labs Nlnetlabs

Products Unbound

Weakness (CWE)

  • CWE-122: : Heap-based Buffer Overflow

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References and research data (JSON)

Vendor product assessments

Showing 32 of 211 vendor product statements; 179 omitted. Read the full vendor advisory.

  • rhcos-aarch64-4.22.9.8.202609291947-0 as a component of Red Hat OpenShift Container Platform 4.22 · fixed

    Vendor assessment for this product only.

    pkg:generic/redhat/[email protected]?arch=aarch64

    • vendor fix: For OpenShift Container Platform 4.22 see the following documentation, which will be updated shortly for this release, for important instructions on how to upgrade your cluster and fully apply this asynchronous errata update: https://docs.redhat.com/en/documentation/openshift_container_platform/4.22/html/release_notes/ You may download the oc tool and use it to inspect release image metadata for x86_64, s390x, ppc64le, and aarch64 architectures. The image digests may be found at https://quay.io/repository/openshift-release-dev/ocp-release?tab=tags. The sha values for the release are as follows: (For x86_64 architecture) The image digest is sha256:9bde31879df303de7db7c100878393a520215f33815d0d9b188e3b4436c876a7 (For s390x architecture) The image digest is sha256:41d57f38fe018b5dcfb3698eb4630f406ec7546f67819d55acd134c3a2e5827a (For ppc64le architecture) The image digest is sha256:160d848722ca2e69777f512ff36adbd5485854b9905e0813aceecf83d549f5a2 (For aarch64 architecture) The image digest is sha256:b040b4af870284b4fcec18283bac700a5d3a0162cec2101a235dfa9a5f005b14 All OpenShift Container Platform 4.22 users are advised to upgrade to these updated packages and images when they are available in the appropriate release channel. To check for available updates, use the OpenShift CLI (oc) or web console. Instructions for upgrading a cluster are available at https://docs.redhat.com/en/documentation/openshift_container_platform/4.22/html-single/updating_clusters/index#updating-cluster-cli. Vendor guidance
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00
  • python3-unbound-debuginfo-0:1.24.2-7.el10_2.6.s390x as a component of Red Hat Enterprise Linux AppStream (v. 10) · fixed

    Vendor assessment for this product only.

    pkg:rpm/redhat/[email protected]_2.6?arch=s390x

    • vendor fix: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 Vendor guidance
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00
  • unbound-anchor-0:1.24.2-7.el10_2.6.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 10) · fixed

    Vendor assessment for this product only.

    pkg:rpm/redhat/[email protected]_2.6?arch=x86_64

    • vendor fix: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 Vendor guidance
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00
  • unbound-debugsource-0:1.24.2-7.el10_2.6.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 10) · fixed

    Vendor assessment for this product only.

    pkg:rpm/redhat/[email protected]_2.6?arch=ppc64le

    • vendor fix: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 Vendor guidance
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00
  • unbound-libs-0:1.24.2-7.el10_2.6.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 10) · fixed

    Vendor assessment for this product only.

    pkg:rpm/redhat/[email protected]_2.6?arch=x86_64

    • vendor fix: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 Vendor guidance
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00
  • unbound-utils-debuginfo-0:1.24.2-7.el10_2.6.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 10) · fixed

    Vendor assessment for this product only.

    pkg:rpm/redhat/[email protected]_2.6?arch=ppc64le

    • vendor fix: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 Vendor guidance
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00
  • python3-unbound-debuginfo-0:1.16.2-5.14.el8_10.4.s390x as a component of Red Hat Enterprise Linux AppStream (v. 8) · fixed

    Vendor assessment for this product only.

    pkg:rpm/redhat/[email protected]_10.4?arch=s390x

    • vendor fix: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 Vendor guidance
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00
  • unbound-debuginfo-0:1.16.2-5.14.el8_10.4.s390x as a component of Red Hat Enterprise Linux AppStream (v. 8) · fixed

    Vendor assessment for this product only.

    pkg:rpm/redhat/[email protected]_10.4?arch=s390x

    • vendor fix: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 Vendor guidance
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00
  • unbound-devel-0:1.16.2-5.14.el8_10.4.s390x as a component of Red Hat Enterprise Linux AppStream (v. 8) · fixed

    Vendor assessment for this product only.

    pkg:rpm/redhat/[email protected]_10.4?arch=s390x

    • vendor fix: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 Vendor guidance
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00
  • unbound-libs-debuginfo-0:1.16.2-5.14.el8_10.4.s390x as a component of Red Hat Enterprise Linux AppStream (v. 8) · fixed

    Vendor assessment for this product only.

    pkg:rpm/redhat/[email protected]_10.4?arch=s390x

    • vendor fix: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 Vendor guidance
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00
  • python3-unbound-debuginfo-0:1.24.2-3.el9_8.8.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 9) · fixed

    Vendor assessment for this product only.

    pkg:rpm/redhat/[email protected]_8.8?arch=x86_64

    • vendor fix: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 Vendor guidance
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00
  • unbound-debuginfo-0:1.24.2-3.el9_8.8.s390x as a component of Red Hat Enterprise Linux AppStream (v. 9) · fixed

    Vendor assessment for this product only.

    pkg:rpm/redhat/[email protected]_8.8?arch=s390x

    • vendor fix: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 Vendor guidance
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00
  • unbound-dracut-0:1.24.2-3.el9_8.8.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 9) · fixed

    Vendor assessment for this product only.

    pkg:rpm/redhat/[email protected]_8.8?arch=x86_64

    • vendor fix: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 Vendor guidance
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00
  • unbound-libs-debuginfo-0:1.24.2-3.el9_8.8.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 9) · fixed

    Vendor assessment for this product only.

    pkg:rpm/redhat/[email protected]_8.8?arch=x86_64

    • vendor fix: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 Vendor guidance
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00
  • unbound-debuginfo-0:1.24.2-7.el10_2.6.ppc64le as a component of Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) · fixed

    Vendor assessment for this product only.

    pkg:rpm/redhat/[email protected]_2.6?arch=ppc64le

    • vendor fix: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 Vendor guidance
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00
  • unbound-devel-0:1.24.2-7.el10_2.6.x86_64 as a component of Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) · fixed

    Vendor assessment for this product only.

    pkg:rpm/redhat/[email protected]_2.6?arch=x86_64

    • vendor fix: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 Vendor guidance
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00
  • python3-unbound-debuginfo-0:1.24.2-3.el9_8.8.i686 as a component of Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) · fixed

    Vendor assessment for this product only.

    pkg:rpm/redhat/[email protected]_8.8?arch=i686

    • vendor fix: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 Vendor guidance
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00
  • unbound-debugsource-0:1.24.2-3.el9_8.8.i686 as a component of Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) · fixed

    Vendor assessment for this product only.

    pkg:rpm/redhat/[email protected]_8.8?arch=i686

    • vendor fix: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 Vendor guidance
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00
  • unbound-libs-debuginfo-0:1.24.2-3.el9_8.8.i686 as a component of Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) · fixed

    Vendor assessment for this product only.

    pkg:rpm/redhat/[email protected]_8.8?arch=i686

    • vendor fix: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 Vendor guidance
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00
  • unbound-anchor-0:1.26.1-1.hum1@x86_64 as a component of Red Hat Hardened Images · fixed

    Vendor assessment for this product only.

    pkg:rpm/redhat/[email protected]?arch=x86_64&distro=hummingbird-20251124&repository_id=public-hummingbird-x86_64-rpms

    • vendor fix: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://images.redhat.com/ Vendor guidance
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00
  • unbound-utils-0:1.26.1-1.hum1@x86_64 as a component of Red Hat Hardened Images · fixed

    Vendor assessment for this product only.

    pkg:rpm/redhat/[email protected]?arch=x86_64&distro=hummingbird-20251124&repository_id=public-hummingbird-x86_64-rpms

    • vendor fix: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://images.redhat.com/ Vendor guidance
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00
  • unbound as a component of Red Hat Enterprise Linux 6 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/unbound

    • no fix planned: Out of support scope
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00
  • unbound-devel as a component of Red Hat Enterprise Linux 6 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/unbound-devel

    • no fix planned: Out of support scope
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00
  • unbound-libs as a component of Red Hat Enterprise Linux 6 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/unbound-libs

    • no fix planned: Out of support scope
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00
  • unbound-python as a component of Red Hat Enterprise Linux 6 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/unbound-python

    • no fix planned: Out of support scope
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00
  • unbound.src as a component of Red Hat Enterprise Linux 6 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/unbound?arch=src

    • no fix planned: Out of support scope
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00
  • unbound as a component of Red Hat Enterprise Linux 7 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/unbound

    • none available: Affected
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00
  • unbound-devel as a component of Red Hat Enterprise Linux 7 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/unbound-devel

    • none available: Affected
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00
  • unbound-libs as a component of Red Hat Enterprise Linux 7 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/unbound-libs

    • none available: Affected
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00
  • unbound-python as a component of Red Hat Enterprise Linux 7 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/unbound-python

    • none available: Affected
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00
  • unbound.src as a component of Red Hat Enterprise Linux 7 · known affected

    Vendor assessment for this product only.

    pkg:rpm/redhat/unbound?arch=src

    • none available: Affected
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00
  • openshift/ose-rhel-coreos-8 as a component of Red Hat OpenShift Container Platform 4 · known affected

    Vendor assessment for this product only.

    pkg:oci/[email protected]?repository_url=registry.redhat.io/openshift/ose-rhel-coreos-8

    • none available: Affected
    Red Hat · CVE-2026-81634 · Updated 2026-10-08T21:10:50+00:00

Known Affected Software Configurations

VendorProductVersion range
NlnetlabsUnbound< 1.26.1

All CVSS metrics

  • HIGH 7.5 v3.1 · CNA Primary
    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  • HIGH 7.5 v3.1 · NVD Secondary
    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

Patches & mitigations

Advisories

Technical & other

Sources: NVD · CVE.org · EPSS