🛡️ CVE-2026-33219 — nats

🟡 CVSS 5.3 — Medium ✅ No Known Exploit CWE-770 NVD
5.3
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

NATS is vulnerable to pre-auth DoS through WebSockets client service

Background

NATS.io is a high performance open source pub-sub distributed communication technology, built for the cloud, on-premise, IoT, and edge computing.

The nats-server offers a WebSockets client service, used in deployments where browsers are the NATS clients.

Problem Description

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 [NATS-advisory-ID 2026-02](https://advisories.nats.io/CVE/secnote-2026-02.txt) (aka CVE-2026-27571; GHSA-qrvq-68c2-7grw).

That earlier issue was a compression bomb, this vulnerability is not. Attacks against this new issue thus require significant client bandwidth.

Affected Versions

Any version before v2.12.6 or v2.11.15

Workarounds

Disable websockets if not required for project deployment.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality none, integrity none, availability low.

Weakness class

CVE-2026-33219 is classified as CWE-770: Allocation of Resources Without Limits. Resources are allocated on request with no cap, so a client can exhaust them.

Affected software

CVE-2026-33219 is recorded against 4 packages.

  • github.com/nats-io/nats-server
  • github.com/nats-io/nats-server/v2
  • nats
  • nats-server (from 2.12.0 up to 2.12.6)

Timeline and source

Published on 24 March 2026 and last revised on 2 April 2026. No public exploit is currently recorded for this entry. Record sourced from NVD.

References

github.com (Web)
nvd.nist.gov (Advisory)
advisories.nats.io (Web)
advisories.nats.io (Web)
github.com (Advisory)
github.com (Package)

CVE-2026-33219 on other distributions

Each distribution ships its own build and its own fixed version. Pick the one you run:

Details

Severity Medium
CVSS Score 5.3
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
CWE CWE-770
Public Exploit ✅ No
Source NVD
Published 2026-03-24
Updated 2026-08-12
Modified 2026-04-02
Fix URL N/A

Affected Packages

Software From version Fixed in
github.com/nats-io/nats-server — —
github.com/nats-io/nats-server/v2 — —
nats — —
nats-server 2.12.0 2.12.6

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