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Fencer Vulns
high 7.5

CVE-2026-42959 json

Crash during DNSSEC validation of malicious content

published 2026-05-20 5 mo ago modified 2026-09-01 2 mo ago also EUVD-2026-31084

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.8%
EPSS 0.8% chance of exploitation in 30 days, percentile 57%
public exploits
0
none known

Summary

NLnet Labs Unbound up to and including version 1.25.0 has a denial of service vulnerability in the DNSSEC validator that can lead to a crash given malicious upstream replies. When Unbound constructs chase-reply messages for validation, the code uses the wrong counter to calculate write offsets for ADDITIONAL section rrsets. DNAME duplication could increase the ANSWER section count and authority filtering could decrease the AUTHORITY section count and create an uninitialized array slot. Combining these two, the validator later dereferences this uninitialized pointer, causing an immediate process crash. An adversary controlling a DNSSEC-signed domain can trigger this bug with a single query by configuring a DNAME chain with unsigned CNAMEs and a response containing unsigned AUTHORITY records alongside signed ADDITIONAL glue records. Unbound 1.25.1 contains a patch with a fix to use the proper counters to calculate the write offsets.

Patch / fix

  • NLnet Labs Unbound 1.25.1
  • Red Hat Red Hat Enterprise Linux 10 0:1.24.2-7.el10_2.1
  • Red Hat Red Hat Enterprise Linux 8 0:1.16.2-5.11.el8_10
  • Red Hat Red Hat Enterprise Linux 9 0:1.24.2-3.el9_8.1
  • Red Hat Red Hat Hardened Images 1.25.1-0.1.hum1
  • unbound Debian 13 1.22.0-2+deb13u3
  • unbound Debian 14 1.25.1-1

debian advisories DEBIAN-CVE-2026-42959

  • unbound Ubuntu 22.04 LTS 1.13.1-1ubuntu5.15
  • unbound Ubuntu 24.04 LTS 1.19.2-1ubuntu3.8
  • unbound Ubuntu 25.10 1.22.0-2ubuntu2.3
  • unbound Ubuntu 26.04 LTS 1.24.2-1ubuntu2.1
  • unbound Ubuntu Pro 14.04 LTS 1.4.22-1ubuntu4.14.04.3+esm3
  • unbound Ubuntu Pro 16.04 LTS 1.5.8-1ubuntu1.1+esm3
  • unbound Ubuntu Pro 18.04 LTS 1.6.7-1ubuntu2.6+esm4
  • unbound Ubuntu Pro 20.04 LTS 1.9.4-2ubuntu1.11+esm1

ubuntu advisories UBUNTU-CVE-2026-42959

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_8.1
  • unbound-libs RHEL 9 1.24.2-3.el9_8.1
  • unbound-dracut RHEL 9 1.24.2-3.el9_8.1
  • python3-unbound RHEL 9 1.24.2-3.el9_8.1
  • unbound RHEL 8 1.16.2-5.11.el8_10
  • unbound-libs RHEL 8 1.16.2-5.11.el8_10
  • python3-unbound RHEL 8 1.16.2-5.11.el8_10
  • unbound RHEL 10.2 1.24.2-7.el10_2.1

red hat advisories RHSA-2026:24369RHSA-2026:24365RHSA-2026:23231RHSA-2026:19752

  • unbound SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 1.24.1-160000.2.1
  • unbound SLES for SAP 15 SP5, SLES for SAP 15 SP4, SLES 15 SP5-LTSS +6 more 1.20.0-150100.10.25.1

suse advisories SUSE-SU-2026:22160-1SUSE-SU-2026:22213-1SUSE-SU-2026:2369-1

  • unbound openSUSE Leap 16.0 1.24.1-160000.2.1
  • unbound openSUSE Tumbleweed 1.25.1-1.1

opensuse advisories openSUSE-SU-2026:21083-1openSUSE-SU-2026:10903-1

  • unbound AlmaLinux 8 1.16.2-5.11.el8_10
  • unbound-libs AlmaLinux 8 1.16.2-5.11.el8_10
  • python3-unbound AlmaLinux 8 1.16.2-5.11.el8_10
  • unbound AlmaLinux 9 1.24.2-3.el9_8.1
  • unbound-libs AlmaLinux 9 1.24.2-3.el9_8.1
  • unbound-dracut AlmaLinux 9 1.24.2-3.el9_8.1
  • python3-unbound AlmaLinux 9 1.24.2-3.el9_8.1
  • unbound AlmaLinux 10 1.24.2-7.el10_2.1

almalinux advisories ALSA-2026:24365ALSA-2026:24369ALSA-2026:23231

  • unbound Rocky Linux 9 1.24.2-3.el9_8.1
  • unbound Rocky Linux 8 1.16.2-5.11.el8_10
  • unbound Rocky Linux 10 1.24.2-7.el10_2.1

rocky linux advisories RLSA-2026:24369RLSA-2026:24365RLSA-2026:23231

  • unbound Alpine 3.23, Alpine 3.22 1.25.2-r0
  • unbound Alpine 3.24 1.25.1-r0

alpine advisories ALPINE-CVE-2026-42959

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • unbound Azure Linux 3.0 1.25.1-1

azure linux advisories AZL-87021

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

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-2026-42959 updated cvss 7.5

unbound: Unbound DNSSEC Validator Denial of Service via Incorrect Write Offset Counter in Chase-Reply Messages

  • Red Hat Enterprise Linux 6 unbound, unbound-libs, unbound-python
    affected: workaround, 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, openshift/ose-rhel-coreos-9
    affected: workaround, no fix available
  • Red Hat Enterprise Linux AppStream (v. 8) unbound 1.16.2-5.11.el8_10, unbound-libs 1.16.2-5.11.el8_10, python3-unbound 1.16.2-5.11.el8_10
    fixed: vendor fix RHSA-2026:24365
  • Red Hat Enterprise Linux AppStream (v. 9) unbound 1.24.2-3.el9_8.1, unbound-libs 1.24.2-3.el9_8.1, unbound-dracut 1.24.2-3.el9_8.1, python3-unbound 1.24.2-3.el9_8.1
    fixed: vendor fix RHSA-2026:24369
  • Red Hat Enterprise Linux AppStream (v. 10) unbound 1.24.2-7.el10_2.1, unbound-libs 1.24.2-7.el10_2.1, unbound-utils 1.24.2-7.el10_2.1, unbound-anchor 1.24.2-7.el10_2.1, unbound-dracut 1.24.2-7.el10_2.1, python3-unbound 1.24.2-7.el10_2.1
    fixed: vendor fix RHSA-2026:23231
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) unbound-devel 1.24.2-3.el9_8.1, unbound-debuginfo 1.24.2-3.el9_8.1, unbound-debugsource 1.24.2-3.el9_8.1, unbound-libs-debuginfo 1.24.2-3.el9_8.1, python3-unbound-debuginfo 1.24.2-3.el9_8.1
    fixed: vendor fix RHSA-2026:24369
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) unbound-devel 1.24.2-7.el10_2.1, unbound-debuginfo 1.24.2-7.el10_2.1, unbound-debugsource 1.24.2-7.el10_2.1, unbound-libs-debuginfo 1.24.2-7.el10_2.1, unbound-utils-debuginfo 1.24.2-7.el10_2.1, unbound-anchor-debuginfo 1.24.2-7.el10_2.1, +1 more
    fixed: vendor fix RHSA-2026:23231
  • Red Hat Hardened Images unbound 1.25.1-0.1.hum1, unbound-libs 1.25.1-0.1.hum1, unbound-munin 1.25.1-0.1.hum1, unbound-utils 1.25.1-0.1.hum1, unbound-anchor 1.25.1-0.1.hum1, unbound-dracut 1.25.1-0.1.hum1, +1 more
    fixed: vendor fix RHSA-2026:19752

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
5 mo ago

Exploit prediction

0.81% chance of exploitation in the next 30 days, higher than 57% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 4.0 8.7 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/U:Red
CISA ADP 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CNA 4.0 8.7 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:Red
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
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
  • Red Hat Red Hat Enterprise Linux 10
  • Red Hat Red Hat Enterprise Linux 8
  • Red Hat Red Hat Enterprise Linux 9
  • Red Hat Red Hat Hardened Images
  • Red Hat Red Hat Enterprise Linux 6
  • Red Hat Red Hat Enterprise Linux 7
  • Red Hat Red Hat OpenShift Container Platform 4

Classification

Weakness
  • CWE-824 Access of Uninitialized Pointer

References

Sources

Fencer Vulns 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.