CVE-2026-41637: In NLnet Labs Unbound 1.22.0 up to and including 1.25.1, client terminated DNS-over-QUIC (DoQ) queries are not

Routine

LOW 3.7REMOTEUPGRADE

CVE-2026-41637 is a low-severity flaw (CVSS 3.7) affecting unbound. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

In NLnet Labs Unbound 1.22.0 up to and including 1.25.1, client terminated DNS-over-QUIC (DoQ) queries are not accounted properly by Unbound resulting in low-cost inflation of the waiting number of replies for already in-flight resolution queries. This results in degradation of resolution service for new clients for already in-flight queries. A malicious actor can exploit the vulnerability by issuing DoQ queries for query names that need resoluti

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	3.7 (Low)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.4% (top 70%)
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: >= 1.22.0 and < 1.25.2

Fixed in: 1.25.2

Safe to downgrade to: a release before 1.22.0

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 1.22.0 (Debian / Ubuntu)

apt-cache madison unbound sudo apt install unbound=<VERSION_BEFORE_1.22.0> 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_1.22.0> 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.

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-2026-41637?

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

Is CVE-2026-41637 being exploited?

CVE-2026-41637 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-2026-41637 affect?

CVE-2026-41637 affects unbound. Severity is low (CVSS 3.7). In NLnet Labs Unbound 1.22.0 up to and including 1.25.1, client terminated DNS-over-QUIC (DoQ) queries are not accounted properly by Unbound resulting in low-cost inflation of the waiting number of replies for already in-flight resolution q

How urgent is CVE-2026-41637?

Priority 25/100. Remotely exploitable, no login, no user action

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References

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