Race condition in Unbound - CVE-2026-77955

Vulnerability identifier: #VU150189

CSH Severity: Low

CVSS v4: 6.3 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-77955

CWE-ID: CWE-362

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote attacker to cause tampered zone contents to be served or stored on disk.

The vulnerability exists due to a race condition caused by asynchronous DS/DNSKEY resolution in ZONEMD validation for configured zones when validating ZONEMD-configured zones located below, but not at, a trust anchor. A remote attacker can exploit the validation window to cause tampered zone contents to become available before integrity verification completes.

When zonefile writing is enabled, data from a failed verification can persist on disk and be reloaded after restart until verification concludes again.

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 15
SUSE Linux Enterprise Server for SAP Applications 15
SUSE Linux Enterprise Desktop 15
SUSE Linux Enterprise Real Time 15
SUSE Linux Enterprise Micro
Basesystem Module
SUSE Package Hub 15
openSUSE Leap
Anolis OS
Fedora
unbound-utils
unbound-libs
unbound-devel
unbound-anchor
unbound
python3-unbound
libunbound8
unbound-debugsource
unbound-anchor-debuginfo
unbound-debuginfo
libunbound8-debuginfo
unbound-python-debuginfo
unbound-munin
libunbound-devel-mini-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-utils - update to 1.17.1-21
unbound-libs - update to 1.17.1-21
unbound-devel - update to 1.17.1-21
unbound-anchor - update to 1.17.1-21
unbound - update to 1.17.1-21
python3-unbound - 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 - 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-anchor-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-debuginfo - 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
libunbound8-debuginfo - 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
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-2026-77955.txt
• https://nlnetlabs.nl/downloads/unbound/patch_CVE-2026-77955_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