WebSocket to MQTT Routing Flaw in NATS Server

Publication date: 2026-07-08

Last updated on: 2026-07-08

Assigner: GitHub, Inc.

Description

NATS Server is a high-performance server for NATS.io, the cloud and edge native messaging system. Prior to 2.14.3 and 2.12.12, a WebSocket listener could route requests for the MQTT-over-WebSocket path into MQTT handling even when MQTT was not configured, allowing an unauthenticated client with access to the WebSocket listener to reach uninitialized MQTT state and crash the server process. This issue is fixed in versions 2.14.3 and 2.12.12.

CVSS Scores

EPSS Scores

Probability:
Percentile:

Meta Information

Published

2026-07-08

Last Modified

2026-07-08

Generated

2026-07-09

AI Q&A

2026-07-09

EPSS Evaluated

N/A

NVD

CVE-2026-58208

Affected Vendors & Products

Vendor	Product	Version / Range
nats_io	nats_server	to 2.12.12 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-248	An exception is thrown from a function, but it is not caught.

Attack-Flow Graph

Executive Summary

This vulnerability exists in the NATS Server, a high-performance messaging server. Before versions 2.14.3 and 2.12.12, the WebSocket listener could mistakenly route requests intended for MQTT-over-WebSocket to the MQTT handler even if MQTT was not configured. This allowed an unauthenticated client with access to the WebSocket listener to reach an uninitialized MQTT state, which could cause the server process to crash.

Impact Analysis

The impact of this vulnerability is a potential denial of service (DoS) condition. An unauthenticated attacker with access to the WebSocket listener can cause the NATS Server to crash by triggering the uninitialized MQTT state, leading to service disruption.

Mitigation Strategies

To mitigate this vulnerability, you should upgrade your NATS Server to version 2.14.3 or 2.12.12 or later, where the issue is fixed.

Hi! I’m here to help you understand CVE-2026-58208. Ask me anything about the vulnerability, its impact, or mitigation strategies.

0/70