CVE-2026-55973: In NLnet Labs Unbound 1.23.0 up to and including 1.25.1, when 'dns-error-reporting: yes' is set, the EDNS Repo

Routine

HIGH 7.5REMOTEUPGRADE

CVE-2026-55973 is a high-severity flaw (CVSS 7.5) affecting unbound. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

In NLnet Labs Unbound 1.23.0 up to and including 1.25.1, when 'dns-error-reporting: yes' is set, the EDNS Report-Channel option (code 18) from the last upstream response is read and uses the option's length as the length of the agent domain. When a domain name check is performed on the agent domain, the returned lenght is not used and if the agent domain is followed by garbage, those bytes are moved onto the tail of the synthetic '_er.' report qu

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.3% (top 80%)
CISA exploited list	No
Weakness	CWE-20
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: >= 1.23.0 and < 1.25.2

Fixed in: 1.25.2

Safe to downgrade to: a release before 1.23.0

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 1.23.0 (Debian / Ubuntu)

apt-cache madison unbound sudo apt install unbound=<VERSION_BEFORE_1.23.0> 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_1.23.0> 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-toolkit-gtk3 · FIXED · 0.122-2.fc46 · FEDORA-2026-d11eb2faf0 · source

sudo dnf upgrade --advisory=FEDORA-2026-d11eb2faf0

Fedora ELN · ntpd-rs · FIXED · 1.7.2-3.eln159 · FEDORA-2026-57e4a99310 · source

sudo dnf upgrade --advisory=FEDORA-2026-57e4a99310

Ubuntu 20.04 · unbound · NOT AFFECTED

Ubuntu 22.04 · unbound · NOT AFFECTED

Ubuntu 24.04 · unbound · NOT AFFECTED

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 · FIXED · unbound-1.24.2-7.el10_2.4

sudo dnf upgrade --advisory=RHSA-2026:55892 rpm -q unbound

RHEL 9 · unbound · FIXED · unbound-1.24.2-3.el9_8.4

sudo dnf upgrade --advisory=RHSA-2026:55841 rpm -q unbound

RHEL 6 · unbound · NOT AFFECTED

RHEL 7 · unbound · NOT AFFECTED

RHEL 8 · unbound · NOT AFFECTED

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-2026-55973?

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

Is CVE-2026-55973 being exploited?

CVE-2026-55973 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-2026-55973 affect?

CVE-2026-55973 affects unbound. Severity is high (CVSS 7.5). In NLnet Labs Unbound 1.23.0 up to and including 1.25.1, when 'dns-error-reporting: yes' is set, the EDNS Report-Channel option (code 18) from the last upstream response is read and uses the option's length as the length of the agent domain

How urgent is CVE-2026-55973?

Priority 36/100. High severity; Remotely exploitable, no login, no user action

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References

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