Use of insufficiently random values in Unbound - CVE-2026-50252

Vulnerability identifier: #VU139227

CSH Severity: Medium

CVSS v4: 8.2 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-50252

CWE-ID: CWE-330

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote attacker to conduct DNS cache poisoning attacks.

The vulnerability exists due to improper randomness management in UDP source port selection when handling DNS queries with the SO_REUSEPORT configuration option enabled. A remote attacker can send queries and observe outgoing source ports to conduct DNS cache poisoning attacks.

The issue occurs because worker threads use disjoint UDP source port subsets, allowing observed outgoing source ports to reveal which thread processed the original query.

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
python3-unbound
unbound-anchor
unbound-debuginfo
unbound-debugsource
unbound-devel
unbound-help
unbound-libs
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
unbound - update to 1.13.2-24
python3-unbound - update to 1.13.2-24
unbound-anchor - update to 1.13.2-24
unbound-debuginfo - update to 1.13.2-24
unbound-debugsource - update to 1.13.2-24
unbound-devel - update to 1.13.2-24
unbound-help - update to 1.13.2-24
unbound-libs - update to 1.13.2-24
unbound - update to 1.25.2-1.fc43
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-debugsource - 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-anchor - 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-2026-50252.txt
• https://nlnetlabs.nl/downloads/unbound/unbound-1.25.2.tar.gz

• Multiple vulnerabilities in Unbound
• Fedora 43 update for unbound
• openEuler update for unbound
• SUSE update for unbound
• SUSE update for unbound