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CVE-2026-33218: NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system

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HIGH 7.5REMOTEWATCHLISTUPGRADE

CVE-2026-33218 is a high-severity flaw (CVSS 7.5) affecting nats-server. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Prior to versions 2.11.15 and 2.12.6, a client which can connect to the leafnode port can crash the nats-server with a certain malformed message pre-authentication. Versions 2.11.15 and 2.12.6 contain a fix. As a workaround, disable leafnode support if not needed or restrict network connections to the leafnode port, if plausible without compromising th

Why this priority

  • High severity
  • Remotely exploitable, no login, no user action
  • On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score7.5 (High)
Attack vectorNetwork (remote)
Attack complexityLow
Privileges neededNone
User interactionNone
EPSS exploit chance0.6% (top 50%)
CISA exploited listNo
WeaknessCWE-20, CWE-1286
Published2026-03-25
Last modified2026-09-09
Publisher (CNA): GitHub, Inc. · Vendor: linuxfoundation

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Last updated 2026-09-09 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

linuxfoundation nats-server UPGRADE
Affected: < 2.11.15 · >= 2.12.0 and < 2.12.6
Fixed in: 2.11.15, 2.12.6
Safe to downgrade to: a release before 2.12.0
1. Check installed version
apt-cache policy nats-server || rpm -q nats-server || nats-server --version
2. UPGRADE to 2.11.15 (Debian / Ubuntu)
sudo apt update && sudo apt install --only-upgrade nats-server
2. UPGRADE (RHEL / Amazon Linux / Fedora)
sudo dnf upgrade nats-server
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 2.12.0 (Debian / Ubuntu)
apt-cache madison nats-server sudo apt install nats-server=<VERSION_BEFORE_2.12.0> sudo apt-mark hold nats-server
3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)
dnf --showduplicates list nats-server sudo dnf downgrade nats-server-<VERSION_BEFORE_2.12.0> sudo dnf versionlock add nats-server
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-2026-33218?

nats-server: upgrade to 2.11.15, 2.12.6. Exact commands for each OS are on this page.

Is CVE-2026-33218 being exploited?

CVE-2026-33218 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-2026-33218 affect?

CVE-2026-33218 affects nats-server. Severity is high (CVSS 7.5). NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Prior to versions 2.11.15 and 2.12.6, a client which can connect to the leafnode port can crash the nats-server with a certain malformed message

How urgent is CVE-2026-33218?

Priority 49/100. High severity; Remotely exploitable, no login, no user action; On your watchlist

Related CVEs

References

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