Incorrect calculation in Unbound - CVE-2026-77860

Vulnerability identifier: #VU150188

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-2026-77860

CWE-ID: CWE-682

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 improper wait-limit counter management in the serve-expired code path when handling queries for expired cached names. A remote attacker can alternate unanswered queries with queries for expired cached names to cause a denial of service.

Exploitation requires control of an authoritative zone with a short TTL so cached entries expire quickly.

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

Install security update from vendor's website.

Unbound - update to 1.26.1
unbound - addressed in versions 1.26.1-1.fc43, 1.26.1-1.fc44, 1.26.1-1.fc45
unbound-devel - addressed in versions 1.26.1-150100.10.31.1, 1.26.1-150600.23.24.1
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-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-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-debuginfo - update to 1.26.1-150600.23.24.1
unbound-python - update to 1.26.1-150600.23.24.1
libunbound-devel-mini-debugsource - 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
unbound (Debian package) - update to 1.26.1-0+deb13u1

• https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-77860.txt
• 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