---
id: CVE-2026-33219
title: >-
  NATS-Server is a High-Performance server for NATS.io, a cloud and edge native
  messaging system
summary: >-
  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-…
severity: medium
cvss: 5.3
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L'
cwe:
  - CWE-770
vendor: linuxfoundation
product: nats-server
affected:
  - nats-server < 2.11.15
  - 'nats-server >= 2.12.0, < 2.12.6'
patched:
  - nats-server 2.12.6
published: '2026-03-25'
updated: '2026-09-09'
sourceUpdated: '2026-09-09T13:19:24.173'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-33219'
references:
  - url: 'https://advisories.nats.io/CVE/secnote-2026-02.txt'
    label: security-advisories@github.com
  - url: 'https://advisories.nats.io/CVE/secnote-2026-11.txt'
    label: security-advisories@github.com
  - url: 'https://github.com/advisories/GHSA-qrvq-68c2-7grw'
    label: security-advisories@github.com
  - url: >-
      https://github.com/nats-io/nats-server/security/advisories/GHSA-8r68-gvr4-jh7j
    label: security-advisories@github.com
  - url: 'https://access.redhat.com/errata/RHSA-2026:21769'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:22347'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:23345'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/security/cve/CVE-2026-33219'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2451445'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33219.json
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-33219'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-33219'
tags:
  - nvd
  - cve.org
  - csaf
  - vex
  - red-hat
  - score-dispute
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-03-25T20:10:18.603979Z'
epss: 0.01
epssPercentile: 0.61262
scores:
  nvd: 5.3
  vendor: 7.5
  cna: 5.3
ingestedAt: '2026-07-20T12:38:40.736Z'
---

## Overview

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 this new issue thus require significant client bandwidth. Versions 2.11.15 and 2.12.6 contain a fix. As a workaround, disable websockets if not required for project deployment.

## Affected

- `nats-server < 2.11.15`
- `nats-server >= 2.12.0, < 2.12.6`

## Remediation

Upgrade past the affected range:

- `nats-server 2.12.6`

## Vendor advisories

- **RHSA-2026:22347** · Red Hat · fixed in: Multicluster Global Hub 1.4.5 · released 2026-06-01 · [advisory](https://access.redhat.com/errata/RHSA-2026:22347)
- **RHSA-2026:23345** · Red Hat · fixed in: Multicluster Global Hub 1.6.5 · released 2026-06-04 · [advisory](https://access.redhat.com/errata/RHSA-2026:23345)
- **RHSA-2026:21769** · Red Hat · fixed in: Red Hat multicluster global hub 1.5.3 · released 2026-05-28 · [advisory](https://access.redhat.com/errata/RHSA-2026:21769)