NATS is vulnerable to MQTT hijacking via Client ID

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 provides an MQTT client interface.

Problem Description

Sessions and Messages can by hijacked via MQTT Client ID malfeasance.

Affected Versions

Any version before v2.12.6 or v2.11.15

Workarounds

None.

Resources

• This document is canonically: https://advisories.nats.io/CVE/secnote-2026-06.txt
• GHSA advisory: https://github.com/nats-io/nats-server/security/advisories/GHSA-fcjp-h8cc-6879
• MITRE CVE entry: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2026-33215