CVE-2026-33219: NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system

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MEDIUM 5.3REMOTEWATCHLISTUPGRADE

CVE-2026-33219 is a medium-severity flaw (CVSS 5.3) 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. Prior to versions 2.11.15 and 2.12.6, a malicious client which can connect to the WebSockets port can cause unbounded memory use in the nats-server before authentication; this requires sending a corresponding amount of data. This is a milder variant of CVE-2026-27571. That earlier issue was a compression bomb, this vulnerability is not. Attacks against

Why this priority

Remotely exploitable, no login, no user action
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	5.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.5% (top 54%)
CISA exploited list	No
Weakness	CWE-770
Published	2026-03-25
Last modified	2026-09-09

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

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

Am I affected?

Timeline

2026-03-25 20:16 UTCPublished CVE record published
2026-09-09 13:19 UTCUpdated Record last modified

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-2026-33219?

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

Is CVE-2026-33219 being exploited?

CVE-2026-33219 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-2026-33219 affect?

CVE-2026-33219 affects nats-server. Severity is medium (CVSS 5.3). 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 malicious client which can connect to the WebSockets port can cause unbounded memory use in the nats-ser

How urgent is CVE-2026-33219?

Priority 40/100. Remotely exploitable, no login, no user action; 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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