CVE-2026-33249: NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system

Routine

MEDIUM 4.3WATCHLISTUPGRADE

CVE-2026-33249 is a medium-severity flaw (CVSS 4.3) 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. Starting in version 2.11.0 and prior to versions 2.11.15 and 2.12.6, a valid client which uses message tracing headers can indicate that the trace messages can be sent to an arbitrary valid subject, including those to which the client does not have publish permission. The payload is a valid trace message and not chosen by the attacker. Versions 2.11.15

Why this priority

On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	4.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.2% (top 85%)
CISA exploited list	No
Weakness	CWE-863
Published	2026-03-25
Last modified	2026-06-17

Publisher (CNA): GitHub, Inc. · Vendor: linuxfoundation

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-03-25 21:16 UTCPublished CVE record published
2026-06-17 10:37 UTCUpdated Record last modified

linuxfoundation nats-server UPGRADE

Affected: >= 2.11.0 and < 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 2.11.0

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 2.11.0 (Debian / Ubuntu)

apt-cache madison nats-server sudo apt install nats-server=<VERSION_BEFORE_2.11.0> 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_2.11.0> 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-2026-33249?

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

Is CVE-2026-33249 being exploited?

CVE-2026-33249 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-2026-33249 affect?

CVE-2026-33249 affects nats-server. Severity is medium (CVSS 4.3). NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. Starting in version 2.11.0 and prior to versions 2.11.15 and 2.12.6, a valid client which uses message tracing headers can indicate that the tra

How urgent is CVE-2026-33249?

Priority 24/100. On your watchlist

Related CVEs

CVE-2026-58210 HIGH 7.5 UPGRADE NATS Server is a high-performance server for NATS.io, the cloud and edge native messaging system
CVE-2026-58250 HIGH 7.5 UPGRADE NATS Server is a high-performance server for NATS.io, the cloud and edge native messaging system
CVE-2026-58208 MEDIUM 6.8 UPGRADE NATS Server is a high-performance server for NATS.io, the cloud and edge native messaging system
CVE-2026-58207 HIGH 7.7 UPGRADE NATS Server is a high-performance server for NATS.io, the cloud and edge native messaging system
CVE-2026-58253 HIGH 8.8 UPGRADE NATS Server is a high-performance server for NATS.io, the cloud and edge native messaging system

References

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