Inefficient Algorithmic Complexity in Unbound - CVE-2026-85501

Vulnerability identifier: #VU150196

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-2026-85501

CWE-ID: CWE-407

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 inefficient algorithmic complexity in the DNSSEC validator's Zone, Algo, KeyTag matching mechanism when processing DNS responses containing numerous mismatched DNSKEY, RRSIG, and DS records. A remote attacker can provide a crafted DNS response to cause a denial of service.

Unbound
SUSE Linux Enterprise Server 15 SP6
SUSE Linux Enterprise Server 15 SP5
SUSE Linux Enterprise Server 15 SP4
Debian Linux
SUSE Linux Enterprise High Performance Computing 15
SUSE Linux Enterprise Server for SAP Applications 15
SUSE Linux Enterprise High Performance Computing ESPOS 15
SUSE Linux Enterprise High Performance Computing LTSS 15
SUSE Linux Enterprise Server 15
SUSE Linux Enterprise Desktop 15
SUSE Linux Enterprise Real Time 15
SUSE Linux Enterprise Micro
Ubuntu
SUSE Package Hub 15
Basesystem Module
openSUSE Leap
Anolis OS
Fedora
libunbound2 (Ubuntu package)
unbound (Ubuntu package)
libunbound8 (Ubuntu package)
unbound-utils
python3-unbound
unbound
unbound-anchor
unbound-devel
unbound-libs
libunbound8-debuginfo
libunbound8
unbound-debuginfo
unbound-anchor-debuginfo
unbound-debugsource
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 1.26.1
libunbound2 (Ubuntu package) - addressed in versions 1.4.22-1ubuntu4.14.04.3+esm5, 1.5.8-1ubuntu1.1+esm5, 1.6.7-1ubuntu2.6+esm6
unbound (Ubuntu package) - addressed in versions 1.4.22-1ubuntu4.14.04.3+esm5, 1.5.8-1ubuntu1.1+esm5, 1.6.7-1ubuntu2.6+esm6, 1.9.4-2ubuntu1.11+esm3, 1.13.1-1ubuntu5.17, 1.19.2-1ubuntu3.12, 1.24.2-1ubuntu2.4
libunbound8 (Ubuntu package) - addressed in versions 1.9.4-2ubuntu1.11+esm3, 1.13.1-1ubuntu5.17, 1.19.2-1ubuntu3.12, 1.24.2-1ubuntu2.4
unbound-utils - update to 1.17.1-21
python3-unbound - update to 1.17.1-21
unbound - update to 1.17.1-21
unbound-anchor - update to 1.17.1-21
unbound-devel - update to 1.17.1-21
unbound-libs - update to 1.17.1-21
unbound - addressed in versions 1.26.1-1.fc43, 1.26.1-1.fc44, 1.26.1-1.fc45
libunbound8-debuginfo - addressed in versions 1.26.1-150100.10.31.1, 1.26.1-150600.23.24.1
libunbound8 - addressed in versions 1.26.1-150100.10.31.1, 1.26.1-150600.23.24.1
unbound-devel - addressed in versions 1.26.1-150100.10.31.1, 1.26.1-150600.23.24.1
unbound-debuginfo - addressed in versions 1.26.1-150100.10.31.1, 1.26.1-150600.23.24.1
unbound-anchor - addressed in versions 1.26.1-150100.10.31.1, 1.26.1-150600.23.24.1
unbound-anchor-debuginfo - addressed in versions 1.26.1-150100.10.31.1, 1.26.1-150600.23.24.1
unbound-debugsource - addressed in versions 1.26.1-150100.10.31.1, 1.26.1-150600.23.24.1
unbound-python-debuginfo - update to 1.26.1-150600.23.24.1
unbound-munin - update to 1.26.1-150600.23.24.1
libunbound-devel-mini-debuginfo - update to 1.26.1-150600.23.24.1
unbound-python - update to 1.26.1-150600.23.24.1
unbound - update to 1.26.1-150600.23.24.1
libunbound-devel-mini - update to 1.26.1-150600.23.24.1
libunbound-devel-mini-debugsource - update to 1.26.1-150600.23.24.1
unbound (Debian package) - update to 1.26.1-0+deb13u1

• https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-85501.txt
• https://nlnetlabs.nl/downloads/unbound/patch_CVE-2026-85501_with.diff
• https://github.com/NLnetLabs/unbound/releases/tag/release-1.26.1

• Multiple vulnerabilities in Unbound
• Fedora 45 update for unbound
• Fedora 44 update for unbound
• Fedora 43 update for unbound
• Debian update for unbound
• SUSE update for unbound
• SUSE update for unbound
• Anolis OS update for unbound
• Ubuntu update for unbound