Improper control of a resource through its lifetime in Unbound - CVE-2026-56444

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Main Vulnerability Database Vulnerabilities #VU139218

Improper control of a resource through its lifetime in Unbound - CVE-2026-56444

Published: July 23, 2026


Vulnerability identifier: #VU139218
CSH Severity: Medium
CVSS v4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-56444
CWE-ID: CWE-664
Exploitation vector: Remote access
Exploit availability: No public exploit available

Vulnerability details

The vulnerability allows a remote attacker to cause a denial of service.

The vulnerability exists due to improper state management in the serve-expired logic when handling duplicate in-flight queries for a client-controlled slow-on-demand authoritative zone. A remote attacker can issue crafted queries to cause a denial of service.

Only configurations with 'serve-expired: yes' and 'serve-expired-client-timeout > discard-timeout > 0' are vulnerable, while the shipped default values make the affected branch unreachable.


Affected software

Unbound
SUSE Linux Enterprise Server 15 SP5
SUSE Linux Enterprise Server 15 SP4
SUSE Linux Enterprise Server 15 SP6
SUSE Linux Enterprise High Performance Computing ESPOS 15
SUSE Linux Enterprise Server 15
SUSE Linux Enterprise Server for SAP Applications 15
SUSE Linux Enterprise High Performance Computing LTSS 15
SUSE Linux Enterprise High Performance Computing 15
SUSE Linux Enterprise Desktop 15
SUSE Linux Enterprise Real Time 15
SUSE Linux Enterprise Micro
SUSE Package Hub 15
Basesystem Module
openSUSE Leap
openEuler
Fedora
unbound-libs
unbound-help
unbound-devel
unbound-debugsource
unbound-debuginfo
python3-unbound
unbound
unbound-anchor
unbound-utils
libunbound8-debuginfo
libunbound8
unbound-anchor-debuginfo
unbound-munin
unbound-python
unbound-python-debuginfo
libunbound-devel-mini-debuginfo
libunbound-devel-mini-debugsource
libunbound-devel-mini

How to mitigate CVE-2026-56444

Install security update from vendor's website.

Unbound - update to 1.25.2
unbound-libs - addressed in versions 1.11.0-26, 1.13.2-26, 1.17.1-20
unbound-help - addressed in versions 1.11.0-26, 1.13.2-26, 1.17.1-20
unbound-devel - addressed in versions 1.11.0-26, 1.13.2-26, 1.17.1-20
unbound-debugsource - addressed in versions 1.11.0-26, 1.13.2-26, 1.17.1-20
unbound-debuginfo - addressed in versions 1.11.0-26, 1.13.2-26, 1.17.1-20
python3-unbound - addressed in versions 1.11.0-26, 1.13.2-26, 1.17.1-20
unbound - addressed in versions 1.11.0-26, 1.13.2-26, 1.17.1-20
unbound-anchor - addressed in versions 1.13.2-26, 1.17.1-20
unbound-utils - update to 1.17.1-20
unbound - update to 1.25.2-1.fc43
unbound-anchor - addressed in versions 1.25.2-150100.10.28.1, 1.25.2-150600.23.19.1
unbound-devel - addressed in versions 1.25.2-150100.10.28.1, 1.25.2-150600.23.19.1
libunbound8-debuginfo - addressed in versions 1.25.2-150100.10.28.1, 1.25.2-150600.23.19.1
libunbound8 - addressed in versions 1.25.2-150100.10.28.1, 1.25.2-150600.23.19.1
unbound-anchor-debuginfo - addressed in versions 1.25.2-150100.10.28.1, 1.25.2-150600.23.19.1
unbound-debuginfo - addressed in versions 1.25.2-150100.10.28.1, 1.25.2-150600.23.19.1
unbound-debugsource - addressed in versions 1.25.2-150100.10.28.1, 1.25.2-150600.23.19.1
unbound-munin - update to 1.25.2-150600.23.19.1
unbound-python - update to 1.25.2-150600.23.19.1
unbound - update to 1.25.2-150600.23.19.1
unbound-python-debuginfo - update to 1.25.2-150600.23.19.1
libunbound-devel-mini-debuginfo - update to 1.25.2-150600.23.19.1
libunbound-devel-mini-debugsource - update to 1.25.2-150600.23.19.1
libunbound-devel-mini - update to 1.25.2-150600.23.19.1

External References

Related Security Bulletins