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.

There are packages installed that are affected by multiple vulnerabilities referenced in the following CVEs:

  - 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, for MQTT deployments using usercodes/passwords: MQTT passwords are
    incorrectly classified as a non-authenticating identity statement (JWT) and exposed via monitoring
    endpoints. Versions 2.11.14 and 2.12.6 contain a fix. As a workaround, ensure monitoring end-points are
    adequately secured. Best practice remains to not expose the monitoring endpoint to the Internet or other
    untrusted network users. (CVE-2026-33216)

  - NATS-Server is a High-Performance server for NATS.io, a cloud and edge native messaging system. The nats-
    server provides an MQTT client interface. Prior to versions 2.11.15 and 2.12.5, Sessions and Messages can
    by hijacked via MQTT Client ID malfeasance. Versions 2.11.15 and 2.12.5 patch the issue. No known
    workarounds are available. (CVE-2026-33215)

  - 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, when using ACLs on message subjects, these ACLs were not applied in the
    `$MQTT.>` namespace, allowing MQTT clients to bypass ACL checks for MQTT subjects. Versions 2.11.15 and
    2.12.6 contain a fix. No known workarounds are available. (CVE-2026-33217)

  - 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 the service offered. (CVE-2026-33218)

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - 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. (CVE-2026-33219)

Note that Nessus relies on the presence of the package as reported by the vendor.

There are packages installed that are affected by a vulnerability referenced in the following CVE:

  - 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. (CVE-2026-33219)

ID	Name	Product	Family	Severity
440289	Alpine: nats-server: security update to 2.12.6-r0	Tenable Cloud Security	Alpine Linux Local Security Checks	high
440289	Alpine: nats-server: security update to 2.12.6-r0	Tenable Self-Hosted Container Security	Alpine Linux Local Security Checks	high
303832	Linux Distros Unpatched Vulnerability : CVE-2026-33219	Nessus	Misc.	medium
439158	SCA: security update for github.com/nats-io/nats-server/v2 (GHSA-8r68-gvr4-jh7j)	Tenable Cloud Security	SCA Checks	high
439158	SCA: security update for github.com/nats-io/nats-server/v2 (GHSA-8r68-gvr4-jh7j)	Tenable Self-Hosted Container Security	SCA Checks	high

Detections

Analytics

CVE-2026-33219

high

Tenable Plugins

high

high

medium

high

high