Heap-based buffer overflow in Unbound - CVE-2026-42944

Vulnerability identifier: #VU131929

CSH Severity: Medium

CVSS v4: 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]

CVE-ID: CVE-2026-42944

CWE-ID: CWE-122

Exploitation vector: Remote access

Exploit availability: No public exploit available

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

The vulnerability exists due to a heap-based buffer overflow in the EDNS option encoder when processing queries containing multiple NSID and/or DNS Cookie EDNS and/or EDNS Padding options. A remote attacker can send a specially crafted query to cause a denial of service.

Only instances with the relevant EDNS options enabled are vulnerable.

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

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 (Red Hat package) - addressed in versions 1.16.2-5.11.el8_10, 1.24.2-3.el9_8.1, 1.24.2-7.el10_2.1
unbound-libs - addressed in versions 1.16.2-9.0.1, 1.17.1-11
unbound-devel - addressed in versions 1.16.2-9.0.1, 1.17.1-11
unbound - addressed in versions 1.16.2-9.0.1, 1.17.1-11
python3-unbound - addressed in versions 1.16.2-9.0.1, 1.17.1-11
unbound-utils - update to 1.17.1-11
unbound-anchor - update to 1.17.1-11
unbound-libs - update to 1.17.1-16
unbound - update to 1.17.1-16
unbound-help - update to 1.17.1-16
python3-unbound - update to 1.17.1-16
unbound-anchor - update to 1.17.1-16
unbound-debuginfo - update to 1.17.1-16
unbound-debugsource - update to 1.17.1-16
unbound-devel - update to 1.17.1-16
unbound-utils - update to 1.17.1-16
unbound-anchor-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
libunbound8-debuginfo - 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
unbound-debugsource - 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-debuginfo - addressed in versions 1.20.0-150100.10.25.1, 1.20.0-150600.23.16.1
unbound-python-debuginfo - 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 - update to 1.20.0-150600.23.16.1
libunbound-devel-mini-debugsource - update to 1.20.0-150600.23.16.1
unbound (Debian package) - update to 1.22.0-2+deb13u3
unbound - addressed in versions 1.25.1-1.fc43, 1.25.1-1.fc44

• https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-42944.txt

• Multiple vulnerabilities in Unbound
• Ubuntu update for unbound
• Fedora 44 update for unbound
• Fedora 43 update for unbound
• Debian update for unbound
• openEuler 24.03 LTS update for unbound
• openEuler 24.03 LTS SP3 update for unbound
• openEuler 24.03 LTS SP1 update for unbound
• Ubuntu update for unbound
• Red Hat Enterprise Linux 10 update for unbound
• SUSE update for unbound
• Red Hat Enterprise Linux 8 update for unbound
• Red Hat Enterprise Linux 9 update for unbound
• FreeBSD update for unbound
• SUSE update for unbound
• Anolis OS update for unbound
• Anolis OS update for unbound
• Multiple vulnerabilities in Meinberg LANTIME Operating System Firmware