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CVE-2026-55973

HIGH 7.5 ALL-YEARS

Published 2026-07-22 · Last modified 2026-07-22 · NLnet Labs · NVD: Analyzed

In NLnet Labs Unbound 1.23.0 up to and including 1.25.1, when 'dns-error-reporting: yes' is set, the EDNS Report-Channel option (code 18) from the last upstream response is read and uses the option's length as the length of the agent domain. When a domain name check is performed on the agent domain, the returned lenght is not used and if the agent domain is followed by garbage, those bytes are moved onto the tail of the synthetic '_er.' report query name. That query name is later used in the iterator via a subquery to send out the DNS Error Report and when Unbound tries to walk that query name during 'find_closest_of_type()', it strips labels using the query name length rather than stopping at the embedded root, walks one byte past it, and feeds the first garbage byte to 'dname_query_hash()' as a label length writing over the stack variable 'labuf'. One ordinary upstream response from a delegated zone the attacker controls is sufficient to terminate the daemon.

ELEVATED IMPACT

Severe if exploited (CVSS 7.5), but no confirmed exploitation. Patch on a normal cadence.

Exploitation likelihood

0.3%chance of exploitation in 30 days · 20th percentile

○ In CISA KEV○ Catalogued PoC◆ SSVC: exploitation none, automatable yes

Impact if exploited

7.5CVSS 3.1 · HIGH · CNA

  • 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.

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Affected

Vendors Nlnet Labs Nlnetlabs

Products Unbound

Weakness (CWE)

  • CWE-20: : Improper Input Validation

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 181 vendor product statements; 149 omitted. Read the full vendor advisory.

  • rhcos-aarch64-4.22.9.8.202608251819-0 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:c987c0017b86a5aed02d5fa854b4649039e7221e14fca2e824dc37b2937ce7b2 (For s390x architecture) The image digest is sha256:e38f225c850f6fdbdaf6ac3ef1f762b1e7068da19ef3cd57a00f72554e3d0a72 (For ppc64le architecture) The image digest is sha256:ea726e65a0f5f8ae5b5fe4ce31f2aa75943c893c91bd75feb644c4042c88865d (For aarch64 architecture) The image digest is sha256:ab1d1b8e7b22fb2a6b3923e6e8fe77b8f0f774c762836a07542b7ed5ad52d86d 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-2026-55973 · Updated 2026-10-08T20:56:17+00:00
  • python3-unbound-0:1.24.2-7.el10_2.4.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]_2.4?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-2026-55973 · Updated 2026-10-08T20:56:17+00:00
  • unbound-anchor-0:1.24.2-7.el10_2.4.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 10) · fixed

    Vendor assessment for this product only.

    pkg:rpm/redhat/[email protected]_2.4?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-2026-55973 · Updated 2026-10-08T20:56:17+00:00
  • unbound-debugsource-0:1.24.2-7.el10_2.4.aarch64 as a component of Red Hat Enterprise Linux AppStream (v. 10) · fixed

    Vendor assessment for this product only.

    pkg:rpm/redhat/[email protected]_2.4?arch=aarch64

    • 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-2026-55973 · Updated 2026-10-08T20:56:17+00:00
  • unbound-libs-0:1.24.2-7.el10_2.4.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]_2.4?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-2026-55973 · Updated 2026-10-08T20:56:17+00:00
  • unbound-utils-debuginfo-0:1.24.2-7.el10_2.4.s390x as a component of Red Hat Enterprise Linux AppStream (v. 10) · fixed

    Vendor assessment for this product only.

    pkg:rpm/redhat/[email protected]_2.4?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-2026-55973 · Updated 2026-10-08T20:56:17+00:00
  • unbound-0:1.24.2-3.el9_8.4.aarch64 as a component of Red Hat Enterprise Linux AppStream (v. 9) · fixed

    Vendor assessment for this product only.

    pkg:rpm/redhat/[email protected]_8.4?arch=aarch64

    • 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-2026-55973 · Updated 2026-10-08T20:56:17+00:00
  • unbound-debugsource-0:1.24.2-3.el9_8.4.i686 as a component of Red Hat Enterprise Linux AppStream (v. 9) · fixed

    Vendor assessment for this product only.

    pkg:rpm/redhat/[email protected]_8.4?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-2026-55973 · Updated 2026-10-08T20:56:17+00:00
  • unbound-libs-0:1.24.2-3.el9_8.4.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 9) · fixed

    Vendor assessment for this product only.

    pkg:rpm/redhat/[email protected]_8.4?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-2026-55973 · Updated 2026-10-08T20:56:17+00:00
  • python3-unbound-debuginfo-0:1.24.2-7.el10_2.4.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]_2.4?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-2026-55973 · Updated 2026-10-08T20:56:17+00:00
  • unbound-debugsource-0:1.24.2-7.el10_2.4.s390x 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]_2.4?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-2026-55973 · Updated 2026-10-08T20:56:17+00:00
  • unbound-utils-debuginfo-0:1.24.2-7.el10_2.4.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]_2.4?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-2026-55973 · Updated 2026-10-08T20:56:17+00:00
  • unbound-debuginfo-0:1.24.2-3.el9_8.4.s390x 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]_8.4?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-2026-55973 · Updated 2026-10-08T20:56:17+00:00
  • unbound-devel-0:1.24.2-3.el9_8.4.x86_64 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]_8.4?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-2026-55973 · Updated 2026-10-08T20:56:17+00:00
  • unbound-anchor-0:1.25.2-0.1.hum1@aarch64 as a component of Red Hat Hardened Images · fixed

    Vendor assessment for this product only.

    pkg:rpm/redhat/[email protected]?arch=aarch64&distro=hummingbird-20251124&repository_id=public-hummingbird-aarch64-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-2026-55973 · Updated 2026-10-08T20:56:17+00:00
  • unbound-utils-0:1.25.2-0.1.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-2026-55973 · Updated 2026-10-08T20:56:17+00:00
  • unbound as a component of Red Hat Enterprise Linux 6 · known not affected

    Vendor assessment for this product only.

    Reason: vulnerable code not present

    pkg:rpm/redhat/unbound

    Red Hat · CVE-2026-55973 · Updated 2026-10-08T20:56:17+00:00
  • unbound-devel as a component of Red Hat Enterprise Linux 6 · known not affected

    Vendor assessment for this product only.

    Reason: vulnerable code not present

    pkg:rpm/redhat/unbound-devel

    Red Hat · CVE-2026-55973 · Updated 2026-10-08T20:56:17+00:00
  • unbound-libs as a component of Red Hat Enterprise Linux 6 · known not affected

    Vendor assessment for this product only.

    Reason: vulnerable code not present

    pkg:rpm/redhat/unbound-libs

    Red Hat · CVE-2026-55973 · Updated 2026-10-08T20:56:17+00:00
  • unbound-python as a component of Red Hat Enterprise Linux 6 · known not affected

    Vendor assessment for this product only.

    Reason: vulnerable code not present

    pkg:rpm/redhat/unbound-python

    Red Hat · CVE-2026-55973 · Updated 2026-10-08T20:56:17+00:00
  • unbound.src as a component of Red Hat Enterprise Linux 6 · known not affected

    Vendor assessment for this product only.

    Reason: vulnerable code not present

    pkg:rpm/redhat/unbound?arch=src

    Red Hat · CVE-2026-55973 · Updated 2026-10-08T20:56:17+00:00
  • unbound as a component of Red Hat Enterprise Linux 7 · known not affected

    Vendor assessment for this product only.

    Reason: vulnerable code not present

    pkg:rpm/redhat/unbound

    Red Hat · CVE-2026-55973 · Updated 2026-10-08T20:56:17+00:00
  • unbound-devel as a component of Red Hat Enterprise Linux 7 · known not affected

    Vendor assessment for this product only.

    Reason: vulnerable code not present

    pkg:rpm/redhat/unbound-devel

    Red Hat · CVE-2026-55973 · Updated 2026-10-08T20:56:17+00:00
  • unbound-libs as a component of Red Hat Enterprise Linux 7 · known not affected

    Vendor assessment for this product only.

    Reason: vulnerable code not present

    pkg:rpm/redhat/unbound-libs

    Red Hat · CVE-2026-55973 · Updated 2026-10-08T20:56:17+00:00
  • unbound-python as a component of Red Hat Enterprise Linux 7 · known not affected

    Vendor assessment for this product only.

    Reason: vulnerable code not present

    pkg:rpm/redhat/unbound-python

    Red Hat · CVE-2026-55973 · Updated 2026-10-08T20:56:17+00:00
  • unbound.src as a component of Red Hat Enterprise Linux 7 · known not affected

    Vendor assessment for this product only.

    Reason: vulnerable code not present

    pkg:rpm/redhat/unbound?arch=src

    Red Hat · CVE-2026-55973 · Updated 2026-10-08T20:56:17+00:00
  • python3-unbound as a component of Red Hat Enterprise Linux 8 · known not affected

    Vendor assessment for this product only.

    Reason: vulnerable code not present

    pkg:rpm/redhat/python3-unbound

    Red Hat · CVE-2026-55973 · Updated 2026-10-08T20:56:17+00:00
  • unbound as a component of Red Hat Enterprise Linux 8 · known not affected

    Vendor assessment for this product only.

    Reason: vulnerable code not present

    pkg:rpm/redhat/unbound

    Red Hat · CVE-2026-55973 · Updated 2026-10-08T20:56:17+00:00
  • unbound-devel as a component of Red Hat Enterprise Linux 8 · known not affected

    Vendor assessment for this product only.

    Reason: vulnerable code not present

    pkg:rpm/redhat/unbound-devel

    Red Hat · CVE-2026-55973 · Updated 2026-10-08T20:56:17+00:00
  • unbound-libs as a component of Red Hat Enterprise Linux 8 · known not affected

    Vendor assessment for this product only.

    Reason: vulnerable code not present

    pkg:rpm/redhat/unbound-libs

    Red Hat · CVE-2026-55973 · Updated 2026-10-08T20:56:17+00:00
  • unbound.src as a component of Red Hat Enterprise Linux 8 · known not affected

    Vendor assessment for this product only.

    Reason: vulnerable code not present

    pkg:rpm/redhat/unbound?arch=src

    Red Hat · CVE-2026-55973 · Updated 2026-10-08T20:56:17+00:00
  • openshift/ose-rhel-coreos-8 as a component of Red Hat OpenShift Container Platform 4 · known not affected

    Vendor assessment for this product only.

    Reason: vulnerable code not present

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

    Red Hat · CVE-2026-55973 · Updated 2026-10-08T20:56:17+00:00

Known Affected Software Configurations

VendorProductVersion range
NlnetlabsUnbound≥ 1.23.0 and < 1.25.2

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

Advisories

Technical & other

Sources: NVD · CVE.org · All sources and attribution · EPSS