Use-after-free in Unbound - CVE-2026-50046

Vulnerability identifier: #VU139231

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-2026-50046

CWE-ID: CWE-416

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 use-after-free in the DNS-over-TLS forwarding logic when handling forwarded queries during TLS handshake error paths. A remote attacker can query records in the appropriate zone while keeping the daemon under pressure to trigger the vulnerable error path and cause a denial of service.

Exploitation requires a stub or forward zone configured for DNS-over-TLS together with a configured authname suffix on the server identification, and transient connectivity failure at a precise time during the handshake.

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

Install security update from vendor's website.

Unbound - update to 1.25.2
python3-unbound - update to 1.17.1-14
unbound - update to 1.17.1-14
unbound-anchor - update to 1.17.1-14
unbound-devel - update to 1.17.1-14
unbound-libs - update to 1.17.1-14
unbound-utils - update to 1.17.1-14
unbound-debugsource - update to 1.17.1-20
unbound-anchor - update to 1.17.1-20
unbound-devel - update to 1.17.1-20
unbound-help - update to 1.17.1-20
unbound-libs - update to 1.17.1-20
unbound-utils - update to 1.17.1-20
unbound - update to 1.17.1-20
python3-unbound - update to 1.17.1-20
unbound-debuginfo - 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

• https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-50046.txt

• Multiple vulnerabilities in Unbound
• Fedora 43 update for unbound
• Anolis OS update for unbound
• openEuler 24.03 LTS SP4 update for unbound
• openEuler 24.03 LTS SP3 update for unbound
• openEuler 24.03 LTS SP1 update for unbound
• SUSE update for unbound
• SUSE update for unbound