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

What is CVE-2026-58208?

CVE-2026-58208 is a medium-severity denial of service vulnerability in nats-io nats-server, published on 8 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

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.

Weakness: CWE-248

Which versions are affected by CVE-2026-58208?

It affects 1 product.

Products include Linuxfoundation Nats-Server.

How do I fix CVE-2026-58208?

Upgrade to a fixed version.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2026-58208 being exploited?

There is no known exploitation of CVE-2026-58208 in the wild and no public exploit code.

Other vulnerabilities in nats-io nats-server

• CVE-2022-28357 NATS nats-server allows directory traversal via unintended path to a management action Critical 9.8
• CVE-2026-58253 NATS Server: Route API Auth Bypass High 8.8
• CVE-2022-24450 Incorrect Authorization in NATS nats-server High 8.8
• CVE-2026-33216 NATS has MQTT plaintext password disclosure High 8.6
• CVE-2026-58207 NATS Server: Remote crash via integer overflow in Connz pagination High 7.7

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as AZL-92247, DEBIAN-CVE-2026-58208, GHSA-p957-7v2w-g93g, UBUNTU-CVE-2026-58208.