CVE-2026-33261: A zone transition from NSEC to NSEC3 might trigger an internal inconsistency and cause a denial of service.

Routine

MEDIUM 5.9REMOTEUPGRADE

CVE-2026-33261 is a medium-severity flaw (CVSS 5.9) affecting recursor. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

A zone transition from NSEC to NSEC3 might trigger an internal inconsistency and cause a denial of service.

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	0.2% (top 85%)
CISA exploited list	No
Weakness	CWE-353
Published	2026-04-22
Last modified	2026-10-26

Publisher (CNA): Open-Xchange · Vendor: powerdns

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-22 10:16 UTCPublished CVE record published
2026-10-26 21:10 UTCUpdated Record last modified

powerdns recursor UPGRADE

Affected: >= 5.2.0 and < 5.2.9 · >= 5.3.0 and < 5.3.6 · 5.4.0

Fixed in: 5.2.9, 5.3.6

Safe to downgrade to: a release before 5.2.0

1. Check installed version

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

2. UPGRADE to 5.2.9 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade recursor

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 5.2.0 (Debian / Ubuntu)

apt-cache madison recursor sudo apt install recursor=<VERSION_BEFORE_5.2.0> sudo apt-mark hold recursor

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

dnf --showduplicates list recursor sudo dnf downgrade recursor-<VERSION_BEFORE_5.2.0> sudo dnf versionlock add recursor

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-2026-33261?

recursor: upgrade to 5.2.9, 5.3.6. Exact commands for each OS are on this page.

Is CVE-2026-33261 being exploited?

CVE-2026-33261 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-2026-33261 affect?

CVE-2026-33261 affects recursor. Severity is medium (CVSS 5.9). A zone transition from NSEC to NSEC3 might trigger an internal inconsistency and cause a denial of service.

How urgent is CVE-2026-33261?

Priority 29/100. Remotely exploitable, no login, no user action

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References

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