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Vulnerability · Published Jul 8, 2026 · Assigned by GitHub_M

CVE-2026-58208NATS Server: MQTT-over-WebSocket Path Can Crash WebSocket-Only JetStream Servers Before MQTT Is Enabled

Medium 6.8

In plain English

A medium-severity security flaw 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 0.6% (higher than 49% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)6.8Medium
Exploit odds (30 days)0.6%top 51.1% 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, 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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Debian:12nats-serverno fix listedDEBIAN-CVE-2026-58208
Debian:13nats-serverno fix listedDEBIAN-CVE-2026-58208
Debian:14nats-server2.14.3-1DEBIAN-CVE-2026-58208
Ubuntu:24.04:LTSnats-serverno fix listedUBUNTU-CVE-2026-58208
Ubuntu:25.10nats-serverno fix listedUBUNTU-CVE-2026-58208
Ubuntu:26.10nats-serverno fix listedUBUNTU-CVE-2026-58208

Affected products (as reported)

VendorProductVersions
nats-io nats-server >= 2.14.0-RC.1, < 2.14.3< 2.12.12

Weakness: CWE-248 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H

References