What’s Vulnerable › Vulnerabilities

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

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-07-08 · updated 2026-10-25
• Weakness: CWE-248

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 products

• nats-io nats-server: from 2.12.0 before 2.12.12; from 2.14.0 before 2.14.3 — fixed in 2.12.12, 2.14.3

How to fix

Upgrade to a fixed version: nats-io nats-server 2.12.12, 2.14.3. Check the vendor advisory for mitigations.

References

• https://github.com/nats-io/nats-server/commit/73b3dd9a5ea0fa7bf08b702338676355b29b5fb4
• https://github.com/nats-io/nats-server/commit/837536b98b3a9280b993282155ff2bdd3ca38c30
• https://github.com/nats-io/nats-server/releases/tag/v2.12.12
• https://github.com/nats-io/nats-server/releases/tag/v2.14.3
• https://github.com/nats-io/nats-server/security/advisories/GHSA-p957-7v2w-g93g

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