Use-after-free in Unbound - CVE-2026-33278

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Main Vulnerability Database Vulnerabilities #VU131924

Use-after-free in Unbound - CVE-2026-33278

Published: May 20, 2026


Vulnerability identifier: #VU131924
CSH Severity: Medium
CVSS v4: 8.2 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-33278
CWE-ID: CWE-416
Exploitation vector: Remote access
Exploit availability: No public exploit available

Vulnerability details

The vulnerability allows a remote attacker to cause a denial of service and potentially execute arbitrary code.

The vulnerability exists due to use-after-free in Unbound DNSSEC validator when processing validation state for DS sub-queries after deep-copying response messages during NSEC3 computational budget exhaustion. A remote attacker can control a malicious signed zone and query a vulnerable resolver to cause a denial of service and potentially execute arbitrary code.

Exploitation requires control of a malicious signed zone.


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

How to mitigate CVE-2026-33278

Install security update from vendor's website.

Unbound - update to 1.25.1
LANTIME Operating System Firmware (LTOS) - update to 7.10.012
unbound (Ubuntu package) - addressed in versions 1.4.22-1ubuntu4.14.04.3+esm3, 1.5.8-1ubuntu1.1+esm3, 1.6.7-1ubuntu2.6+esm4, 1.9.4-2ubuntu1.11+esm1, 1.13.1-1ubuntu5.15, 1.19.2-1ubuntu3.8, 1.22.0-2ubuntu2.3, 1.24.2-1ubuntu2.1
unbound-libs - addressed in versions 1.11.0-22, 1.13.2-22, 1.17.1-16
unbound - addressed in versions 1.11.0-22, 1.13.2-22, 1.17.1-16
python3-unbound - addressed in versions 1.11.0-22, 1.13.2-22, 1.17.1-16
unbound-debuginfo - addressed in versions 1.11.0-22, 1.13.2-22, 1.17.1-16
unbound-debugsource - addressed in versions 1.11.0-22, 1.13.2-22, 1.17.1-16
unbound-devel - addressed in versions 1.11.0-22, 1.13.2-22, 1.17.1-16
unbound-help - addressed in versions 1.11.0-22, 1.13.2-22, 1.17.1-16
unbound-anchor - addressed in versions 1.13.2-22, 1.17.1-16
unbound-utils - update to 1.17.1-11
unbound - update to 1.17.1-11
unbound-anchor - update to 1.17.1-11
unbound-devel - update to 1.17.1-11
unbound-libs - update to 1.17.1-11
python3-unbound - update to 1.17.1-11
unbound-utils - update to 1.17.1-16
unbound-debuginfo - addressed in versions 1.20.0-150100.10.25.1, 1.20.0-150600.23.16.1
libunbound8 - addressed in versions 1.20.0-150100.10.25.1, 1.20.0-150600.23.16.1
unbound-anchor-debuginfo - addressed in versions 1.20.0-150100.10.25.1, 1.20.0-150600.23.16.1
unbound-debugsource - addressed in versions 1.20.0-150100.10.25.1, 1.20.0-150600.23.16.1
unbound-anchor - addressed in versions 1.20.0-150100.10.25.1, 1.20.0-150600.23.16.1
libunbound8-debuginfo - addressed in versions 1.20.0-150100.10.25.1, 1.20.0-150600.23.16.1
unbound-devel - addressed in versions 1.20.0-150100.10.25.1, 1.20.0-150600.23.16.1
libunbound-devel-mini - update to 1.20.0-150600.23.16.1
unbound-munin - update to 1.20.0-150600.23.16.1
unbound - update to 1.20.0-150600.23.16.1
libunbound-devel-mini-debuginfo - update to 1.20.0-150600.23.16.1
unbound-python - update to 1.20.0-150600.23.16.1
libunbound-devel-mini-debugsource - update to 1.20.0-150600.23.16.1
unbound-python-debuginfo - update to 1.20.0-150600.23.16.1
unbound (Debian package) - update to 1.22.0-2+deb13u3
unbound (Red Hat package) - addressed in versions 1.24.2-3.el9_8.1, 1.24.2-7.el10_2.1
unbound - addressed in versions 1.25.1-1.fc43, 1.25.1-1.fc44

External References

Related Security Bulletins