Heap-based buffer overflow in Unbound - CVE-2026-81634

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Main Vulnerability Database Vulnerabilities #VU150192

Heap-based buffer overflow in Unbound - CVE-2026-81634

Published: September 16, 2026 / Updated: September 19, 2026


Vulnerability identifier: #VU150192
CSH Severity: Low
CVSS v4: 0 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-81634
CWE-ID: CWE-122
Exploitation vector: Remote access
Exploit availability: No public exploit available

Vulnerability details

The vulnerability allows a remote attacker to cause memory corruption.

The vulnerability exists due to improper buffer length validation in the RRSet canonicalisation routine when processing a 255-length query name with a large TCP response. A remote attacker can provide a crafted DNS response to cause memory corruption.

Canonicalisation occurs before DNSSEC validation.


Affected software

Unbound
SUSE Linux Enterprise Server 15 SP6
SUSE Linux Enterprise Server 15 SP5
SUSE Linux Enterprise Server 15 SP4
Debian Linux
SUSE Linux Enterprise High Performance Computing 15
SUSE Linux Enterprise Server for SAP Applications 15
SUSE Linux Enterprise Server 15
SUSE Linux Enterprise High Performance Computing LTSS 15
SUSE Linux Enterprise High Performance Computing ESPOS 15
SUSE Linux Enterprise Desktop 15
SUSE Linux Enterprise Real Time 15
SUSE Linux Enterprise Micro
Anolis OS
Red Hat Enterprise Linux for ARM 64
Red Hat Enterprise Linux for Power, little endian
Red Hat Enterprise Linux for IBM z Systems
Red Hat Enterprise Linux for x86_64
Ubuntu
Basesystem Module
SUSE Package Hub 15
openSUSE Leap
openEuler
Fedora
libunbound2 (Ubuntu package)
unbound (Ubuntu package)
libunbound8 (Ubuntu package)
unbound
python3-unbound
unbound-anchor
unbound-debuginfo
unbound-debugsource
unbound-devel
unbound-help
unbound-libs
unbound (Red Hat package)
unbound-utils
unbound-anchor-debuginfo
libunbound8
libunbound8-debuginfo
unbound-munin
unbound-python-debuginfo
unbound-python
libunbound-devel-mini-debugsource
libunbound-devel-mini
libunbound-devel-mini-debuginfo
unbound (Debian package)
Red Hat OpenShift Container Platform

How to mitigate CVE-2026-81634

Install security update from vendor's website.

Unbound - update to 1.26.1
libunbound2 (Ubuntu package) - addressed in versions 1.4.22-1ubuntu4.14.04.3+esm5, 1.5.8-1ubuntu1.1+esm5, 1.6.7-1ubuntu2.6+esm6
unbound (Ubuntu package) - addressed in versions 1.4.22-1ubuntu4.14.04.3+esm5, 1.5.8-1ubuntu1.1+esm5, 1.6.7-1ubuntu2.6+esm6, 1.9.4-2ubuntu1.11+esm3, 1.13.1-1ubuntu5.17, 1.19.2-1ubuntu3.12, 1.24.2-1ubuntu2.4
libunbound8 (Ubuntu package) - addressed in versions 1.9.4-2ubuntu1.11+esm3, 1.13.1-1ubuntu5.17, 1.19.2-1ubuntu3.12, 1.24.2-1ubuntu2.4
unbound - addressed in versions 1.13.2-28, 1.17.1-22
python3-unbound - addressed in versions 1.13.2-28, 1.17.1-22
unbound-anchor - addressed in versions 1.13.2-28, 1.17.1-22
unbound-debuginfo - addressed in versions 1.13.2-28, 1.17.1-22
unbound-debugsource - addressed in versions 1.13.2-28, 1.17.1-22
unbound-devel - addressed in versions 1.13.2-28, 1.17.1-22
unbound-help - addressed in versions 1.13.2-28, 1.17.1-22
unbound-libs - addressed in versions 1.13.2-28, 1.17.1-22
unbound (Red Hat package) - addressed in versions 1.16.2-5.14.el8_10.4, 1.24.2-3.el9_8.8, 1.24.2-7.el10_2.6
unbound-devel - addressed in versions 1.16.2-9.0.5, 1.17.1-21
unbound - addressed in versions 1.16.2-9.0.5, 1.17.1-21
unbound-libs - addressed in versions 1.16.2-9.0.5, 1.17.1-21
python3-unbound - addressed in versions 1.16.2-9.0.5, 1.17.1-21
unbound-utils - update to 1.17.1-21
unbound-anchor - update to 1.17.1-21
unbound-utils - update to 1.17.1-22
unbound - addressed in versions 1.26.1-1.fc43, 1.26.1-1.fc44, 1.26.1-1.fc45
unbound-anchor-debuginfo - addressed in versions 1.26.1-150100.10.31.1, 1.26.1-150600.23.24.1
unbound-debugsource - addressed in versions 1.26.1-150100.10.31.1, 1.26.1-150600.23.24.1
unbound-anchor - addressed in versions 1.26.1-150100.10.31.1, 1.26.1-150600.23.24.1
unbound-debuginfo - addressed in versions 1.26.1-150100.10.31.1, 1.26.1-150600.23.24.1
unbound-devel - addressed in versions 1.26.1-150100.10.31.1, 1.26.1-150600.23.24.1
libunbound8 - addressed in versions 1.26.1-150100.10.31.1, 1.26.1-150600.23.24.1
libunbound8-debuginfo - addressed in versions 1.26.1-150100.10.31.1, 1.26.1-150600.23.24.1
unbound-munin - update to 1.26.1-150600.23.24.1
unbound-python-debuginfo - update to 1.26.1-150600.23.24.1
unbound-python - update to 1.26.1-150600.23.24.1
libunbound-devel-mini-debugsource - update to 1.26.1-150600.23.24.1
unbound - update to 1.26.1-150600.23.24.1
libunbound-devel-mini - update to 1.26.1-150600.23.24.1
libunbound-devel-mini-debuginfo - update to 1.26.1-150600.23.24.1
Red Hat OpenShift Container Platform - update to 4.22.17
unbound (Debian package) - update to 1.26.1-0+deb13u1

External References

Related Security Bulletins