CVE-2026-58211

NATS Server: `no_auth_user` pre-CONNECT fast path bypasses user connection restrictions

State: Published
Severity: 5.4 Medium
Published: Jul 8, 2026
Updated: Jul 9, 2026
Reserved: Jun 29, 2026

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.

Scores

CVSS	Score	Vector	Source
3.1	5.4 Medium	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N	GitHub_M

Weaknesses

CWE-863 Incorrect Authorization

Affected Products

Product	Versions
nats-servernats-io	< 2.12.12Affected >= 2.14.0-RC.1, < 2.14.3Affected

References

https://github.com/nats-io/nats-server/security/advisories/GHSA-hmmp-q8cx-v964

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