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Vulnerability · Published Mar 25, 2026 · Assigned by GitHub_M

CVE-2026-33217NATS allows MQTT clients to bypass ACL checks

High 7.1

In plain English

A high-severity incorrect authorization in nats-server from nats-io. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 18% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.1High
Exploit odds (30 days)0.3%top 81.6% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Alpine:v3.23nats-server2.12.6-r0ALPINE-CVE-2026-33217
Alpine:v3.24nats-server2.12.6-r0ALPINE-CVE-2026-33217
Debian:12nats-serverno fix listedDEBIAN-CVE-2026-33217
Debian:13nats-serverno fix listedDEBIAN-CVE-2026-33217
Debian:14nats-server2.12.6-1DEBIAN-CVE-2026-33217
Gogithub.com/nats-io/nats-serverno fix listedGHSA-jxxm-27vp-c3m5
Gogithub.com/nats-io/nats-serverno fix listedGO-2026-4834
Gogithub.com/nats-io/nats-server/v22.11.15, 2.12.6GO-2026-4834
Gogithub.com/nats-io/nats-server/v22.11.15GHSA-jxxm-27vp-c3m5
Gogithub.com/nats-io/nats-server/v22.12.6GHSA-jxxm-27vp-c3m5
Ubuntu:24.04:LTSnats-serverno fix listedUBUNTU-CVE-2026-33217
Ubuntu:25.10nats-serverno fix listedUBUNTU-CVE-2026-33217
Ubuntu:26.10nats-serverno fix listedUBUNTU-CVE-2026-33217

Affected products (as reported)

VendorProductVersions
nats-io nats-server < 2.11.15>= 2.12.0-RC.1, < 2.12.6

Weakness: CWE-863, CWE-425 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:N

References