CVE-2026-50252: In NLnet Labs Unbound 1.4.22 up to and including 1.25.1, UDP source port is randomized and intended to serve a

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CRITICAL 9.3UPGRADE

CVE-2026-50252 is a critical-severity flaw (CVSS 9.3) affecting unbound. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

In NLnet Labs Unbound 1.4.22 up to and including 1.25.1, UDP source port is randomized and intended to serve as a secret value that increases the entropy of DNS transactions. When resolver load balancing policies depend on the source port while their outcome is revealed this secrecy is undermined. The vulnerability arises when the load balancing policy is consistent with respect to the incoming source UDP port and IP address while heavily dependi

Why this priority

Critical severity

A fixed release or distro patch exists.

Risk facts

CVSS score	9.3 (Critical)
Attack vector	Adjacent network
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.2% (top 94%)
CISA exploited list	No
Weakness	CWE-349
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: >= 1.4.22 and < 1.25.2

Fixed in: 1.25.2

Safe to downgrade to: a release before 1.4.22

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 1.4.22 (Debian / Ubuntu)

apt-cache madison unbound sudo apt install unbound=<VERSION_BEFORE_1.4.22> 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_1.4.22> 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-abacus · FIXED · 61-18.fc46 · FEDORA-2026-b1e9de9204 · source

sudo dnf upgrade --advisory=FEDORA-2026-b1e9de9204

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 · FIXED · unbound-1.24.2-7.el10_2.5

sudo dnf upgrade --advisory=RHSA-2026:68291 rpm -q unbound

RHEL 8 · unbound · FIXED · unbound-1.16.2-5.14.el8_10.2

sudo dnf upgrade --advisory=RHSA-2026:69120 rpm -q unbound

RHEL 9 · unbound · FIXED · unbound-1.24.2-3.el9_8.6

sudo dnf upgrade --advisory=RHSA-2026:68292 rpm -q unbound

RHEL 6 · unbound · NOT AFFECTED

RHEL 7 · unbound · NO FIX YET

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

Amazon Linux 2023 · see advisory · FIXED · ALAS2023-2026-2033 · source

sudo dnf update --advisory=ALAS2023-2026-2033

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-2026-50252?

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

Is CVE-2026-50252 being exploited?

CVE-2026-50252 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-2026-50252 affect?

CVE-2026-50252 affects unbound. Severity is critical (CVSS 9.3). In NLnet Labs Unbound 1.4.22 up to and including 1.25.1, UDP source port is randomized and intended to serve as a secret value that increases the entropy of DNS transactions. When resolver load balancing policies depend on the source port w

How urgent is CVE-2026-50252?

Priority 34/100. Critical severity

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References

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