CVE-2026-58208

NATS Server: MQTT-over-WebSocket Path Can Crash WebSocket-Only JetStream Servers Before MQTT Is Enabled

CVE-2026-58208 is fixed in nats-server on 1 platform by DEBIAN-CVE-2026-58208 (version 2.14.3-1), released July 6, 2026. It is not reported as exploited. Patch Radar priority: High.

High

CVSS

7.5

Moderate

Exploitation

None reported

No vendor assessment

CISA KEV

Not listed

Not in the Known Exploited Vulnerabilities catalog

EPSS

0.0060

49th percentile

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.

Where it's fixed

Product	Fixed in	Fix	Released
Linux
nats-server · Debian 14	2.14.3-1	DEBIAN-CVE-2026-58208	Jul 6, 2026

Details

Published
July 8, 2026
Weakness
Uncaught Exception
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Vendor advisory
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-58208

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