CVE-2026-58211— NATS Server: `no_auth_user` pre-CONNECT fast path bypasses user connection restrictions
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团队开源的一个云原生消息系统。 NATS Server 2.12.12之前版本和2.14.0-RC.1至2.14.3之前版本存在授权问题漏洞，该漏洞源于解析器路径问题，在首次客户端操作非CONNECT时可将客户端注册为配置的no_auth_user，绕过身份验证正常应用的用户级连接限制（如allowed_connection_types或proxy_required）。
Possible ATT&CK Techniques 1 AI
T1133 · External Remote ServicesAffected Version Matrix 2
| Vendor | Product | Version Range | Status |
|---|---|---|---|
| nats-io | nats-server | < 2.12.12 |
affected |
>= 2.14.0-RC.1, < 2.14.3 |
affected |
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I. Basic Information for CVE-2026-58211
Vulnerability Information
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Vulnerability Title
NATS Server: `no_auth_user` pre-CONNECT fast path bypasses user connection restrictions
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 client could be registered as the configured no_auth_user through a parser path used when the first client operation was not CONNECT, bypassing user-level connection restrictions such as allowed_connection_types or proxy_required that normal authentication would apply. 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:L/PR:L/UI:N/S:U/C:L/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
授权机制不正确
Source: CVE Program / CVE List V5
Vulnerability Title
NATS Server 授权问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
NATS Server是Nats团队开源的一个云原生消息系统。 NATS Server 2.12.12之前版本和2.14.0-RC.1至2.14.3之前版本存在授权问题漏洞，该漏洞源于解析器路径问题，在首次客户端操作非CONNECT时可将客户端注册为配置的no_auth_user，绕过身份验证正常应用的用户级连接限制（如allowed_connection_types或proxy_required）。
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 | < 2.12.12 | - |
|
II. Public POCs for CVE-2026-58211
| # | POC Description | Source Link | Shenlong Link |
|---|
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Vendor Advisories for CVE-2026-58211 (1)
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-2026-58208 | 6.8 MEDIUM | NATS Server: MQTT-over-WebSocket Path Can Crash WebSocket-Only JetStream Servers Before MQ |
| 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-2026-58214 | 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
-
CVE-2026-58208
NATS Server: MQTT-over-WebSocket Path Can Crash WebSocket-On -
CVE-2026-58207
NATS Server: Remote crash via integer overflow in Connz pagi -
CVE-2026-58210
NATS Server: MQTT partial CONNECT packets can exhaust pre-au -
CVE-2026-58209
NATS Server: MQTT retained and QoS replay bypass subscribe d -
CVE-2026-58214
NATS Server: MQTT subscribe ACL bypass via $MQTT.deliver.pub
Same vendor: nats-io
-
CVE-2026-58208
NATS Server: MQTT-over-WebSocket Path Can Crash WebSocket-On -
CVE-2026-58207
NATS Server: Remote crash via integer overflow in Connz pagi -
CVE-2026-58210
NATS Server: MQTT partial CONNECT packets can exhaust pre-au -
CVE-2026-58209
NATS Server: MQTT retained and QoS replay bypass subscribe d -
CVE-2026-58214
NATS Server: MQTT subscribe ACL bypass via $MQTT.deliver.pub
Same weakness: CWE-863
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