What’s Vulnerable › Vulnerabilities

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

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-03-25 · updated 2026-09-09
• Weakness: CWE-863

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 products

• nats-io nats-server: before 2.11.15; from 2.12.0 before 2.12.6 — fixed in 2.11.15, 2.12.6

How to fix

Upgrade to a fixed version: nats-io nats-server 2.11.15, 2.12.6. Check the vendor advisory for mitigations.

References

• https://advisories.nats.io/CVE/secnote-2026-07.txt
• https://github.com/nats-io/nats-server/security/advisories/GHSA-jxxm-27vp-c3m5
• https://access.redhat.com/errata/RHSA-2026:21769
• https://access.redhat.com/errata/RHSA-2026:22347
• https://access.redhat.com/errata/RHSA-2026:23345
• https://access.redhat.com/security/cve/CVE-2026-33217
• https://bugzilla.redhat.com/show_bug.cgi?id=2451446
• https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33217.json

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