CVE-2026-56444: In NLnet Labs Unbound 1.20.0 up to and including 1.25.1, when Unbound is configured with 'serve-expired: yes'

Routine

MEDIUM 5.9REMOTEUPGRADE

CVE-2026-56444 is a medium-severity flaw (CVSS 5.9) affecting unbound. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

In NLnet Labs Unbound 1.20.0 up to and including 1.25.1, when Unbound is configured with 'serve-expired: yes' and 'serve-expired-client-timeout > discard-timeout > 0' (contrary to the suggested values), the discard-timeout branch during the serve expired logic drops an aged client reply without performing the correct accounting for the number of reply addresses for the query. Other identical branches outside of serve expired perform the correct d

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.9 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.4% (top 71%)
CISA exploited list	No
Weakness	CWE-772
Published	2026-07-22
Last modified	2026-10-24

Publisher (CNA): NLnet Labs · Vendor: nlnetlabs

Last updated 2026-10-24 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-22 14:17 UTCPublished CVE record published
2026-10-24 13:10 UTCUpdated Record last modified

nlnetlabs unbound UPGRADE

Affected: >= 1.20.0 and < 1.25.2

Fixed in: 1.25.2

Safe to downgrade to: a release before 1.20.0

1. Check installed version

apt-cache policy unbound || rpm -q unbound || unbound --version

2. UPGRADE to 1.25.2 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade unbound

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade unbound

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 1.20.0 (Debian / Ubuntu)

apt-cache madison unbound sudo apt install unbound=<VERSION_BEFORE_1.20.0> sudo apt-mark hold unbound

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list unbound sudo dnf downgrade unbound-<VERSION_BEFORE_1.20.0> sudo dnf versionlock add unbound

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Exact fixes by distribution

Fedora 46 · sugar-calculator · FIXED · 47-14.fc46 · FEDORA-2026-38eeb9e279 · source

sudo dnf upgrade --advisory=FEDORA-2026-38eeb9e279

Fedora ELN · selinux-policy · FIXED · 45.23-1.eln159 · FEDORA-2026-3668c969a2 · source

sudo dnf upgrade --advisory=FEDORA-2026-3668c969a2

Debian 12 · unbound · NO FIX YET

Debian 13 · unbound · FIXED · 1.26.1-0+deb13u1

sudo apt update && sudo apt install --only-upgrade unbound dpkg --compare-versions "$(dpkg-query -W -f='${Version}' unbound)" ge "1.26.1-0+deb13u1" && echo PATCHED || echo STILL-VULNERABLE

RHEL 10 · unbound · DEFERRED

RHEL 6 · unbound · NOT AFFECTED

RHEL 7 · unbound · NOT AFFECTED

RHEL 8 · unbound · NOT AFFECTED

RHEL 9 · unbound · DEFERRED

Alpine 3.22 · unbound · FIXED · unbound-1.25.2-r0

apk add --upgrade unbound apk info -v unbound

Alpine 3.23 · unbound · FIXED · unbound-1.25.2-r0

apk add --upgrade unbound apk info -v unbound

Alpine 3.24 · unbound · FIXED · unbound-1.25.2-r0

apk add --upgrade unbound apk info -v unbound

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-56444?

unbound: upgrade to 1.25.2. Exact commands for each OS are on this page.

Is CVE-2026-56444 being exploited?

CVE-2026-56444 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-56444 affect?

CVE-2026-56444 affects unbound. Severity is medium (CVSS 5.9). In NLnet Labs Unbound 1.20.0 up to and including 1.25.1, when Unbound is configured with 'serve-expired: yes' and 'serve-expired-client-timeout > discard-timeout > 0' (contrary to the suggested values), the discard-timeout branch during the

How urgent is CVE-2026-56444?

Priority 33/100. Remotely exploitable, no login, no user action

Related CVEs

CVE-2026-32665 HIGH 7.5 UPGRADE In NLnet Labs Unbound 1.22.0 up to and including 1.25.1, when downstream DNS-over-QUIC (DoQ) is enabled, the f
CVE-2026-40691 HIGH 7.5 UPGRADE In Unbound 1.9.0 up to and including 1.25.1, when a DNSCrypt query is received over TCP, the routine that encr
CVE-2026-55973 HIGH 7.5 UPGRADE In NLnet Labs Unbound 1.23.0 up to and including 1.25.1, when 'dns-error-reporting: yes' is set, the EDNS Repo
CVE-2026-50252 CRITICAL 9.3 UPGRADE In NLnet Labs Unbound 1.4.22 up to and including 1.25.1, UDP source port is randomized and intended to serve a
CVE-2026-50045 MEDIUM 5.3 UPGRADE In NLnet Labs Unbound 1.22.0 up to and including 1.25.1, a single client query for a deeply nested name under

References

← Back to latest CVEs