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

Quick assessment

Affected
nats-io nats-server
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Nats Server是Nats团队的一款服务端软件产品。 Nats Server 2.14.3之前版本和2.12.12之前版本存在异常处理不当漏洞，该漏洞源于WebSocket监听器在MQTT未配置时仍路由MQTT-over-WebSocket请求，允许未经身份验证的客户端访问未初始化的MQTT状态并导致服务器进程崩溃。

CVSS 6.8 · Medium EPSS 0.60% · P47

Possible ATT&CK Techniques 1 AI

T1496 · Resource Hijacking

Affected Version Matrix 2

VendorProduct Version RangeStatus
nats-io nats-server >= 2.14.0-RC.1, < 2.14.3 affected
< 2.12.12 affected
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I. Basic Information for CVE-2026-58208

Vulnerability Information
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Vulnerability Title
NATS Server: MQTT-over-WebSocket Path Can Crash WebSocket-Only JetStream Servers Before MQTT Is Enabled
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
未捕获的异常
Source: CVE Program / CVE List V5
Vulnerability Title
Nats Server 异常处理不当漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Nats Server是Nats团队的一款服务端软件产品。 Nats Server 2.14.3之前版本和2.12.12之前版本存在异常处理不当漏洞，该漏洞源于WebSocket监听器在MQTT未配置时仍路由MQTT-over-WebSocket请求，允许未经身份验证的客户端访问未初始化的MQTT状态并导致服务器进程崩溃。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
nats-io nats-server >= 2.14.0-RC.1, < 2.14.3 -

II. Public POCs for CVE-2026-58208

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III. Intelligence Information for CVE-2026-58208

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Patches & Fixes for CVE-2026-58208 (2)

Vendor Advisories for CVE-2026-58208 (1)

Vendor Pages for CVE-2026-58208 (2)

Same Patch Batch · nats-io · 2026-07-08 · 12 CVEs total

CVE-2026-58253 8.8 HIGH NATS Server: Route API Auth Bypass
CVE-2026-58207 7.7 HIGH NATS Server: Remote crash via integer overflow in Connz pagination
CVE-2026-58250 7.5 HIGH NATS Server: Pre-auth server crash via double INFO in leafnode handshake
CVE-2026-58210 7.5 HIGH NATS Server: MQTT partial CONNECT packets can exhaust pre-auth memory
CVE-2026-58213 7.1 HIGH NATS Server: MQTT SUBSCRIBE Protocol Injection via Leaf Node/Route Forwarding allows arbit
CVE-2026-58251 6.5 MEDIUM NATS Server: Queue Subscribe Authz Bypass
CVE-2026-58252 6.5 MEDIUM NATS Server: Subscribe Authz Bypass via Wildcard-Overlap
CVE-2026-58211 5.4 MEDIUM NATS Server: `no_auth_user` pre-CONNECT fast path bypasses user connection restrictions
CVE-2026-58214 4.3 MEDIUM NATS Server: MQTT subscribe ACL bypass via $MQTT.deliver.pubrel prefix (incomplete fix for
CVE-2026-58209 4.3 MEDIUM NATS Server: MQTT retained and QoS replay bypass subscribe deny filters
CVE-2026-58254 NATS Server: Incomplete fix for CVE-2026-33249: Leaf node connections bypass Nats-Trace-De

IV. Related Vulnerabilities

Same product: nats-server
Same vendor: nats-io
Same weakness: CWE-248

V. Comments for CVE-2026-58208

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