Vulnerability · Published Jul 8, 2026 · Assigned by GitHub_M

CVE-2026-58211NATS Server: `no_auth_user` pre-CONNECT fast path bypasses user connection restrictions

Medium 5.4

In plain English

A medium-severity incorrect authorization in nats-server from nats-io. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 22% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.4Medium

Exploit odds (30 days)0.3%top 78.1% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

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 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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:12	nats-server	no fix listed	DEBIAN-CVE-2026-58211
Debian:13	nats-server	no fix listed	DEBIAN-CVE-2026-58211
Debian:14	nats-server	2.14.3-1	DEBIAN-CVE-2026-58211
Ubuntu:24.04:LTS	nats-server	no fix listed	UBUNTU-CVE-2026-58211
Ubuntu:25.10	nats-server	no fix listed	UBUNTU-CVE-2026-58211
Ubuntu:26.10	nats-server	no fix listed	UBUNTU-CVE-2026-58211

Affected products (as reported)

Vendor	Product	Versions
nats-io	nats-server	< 2.12.12>= 2.14.0-RC.1, < 2.14.3

Weakness: CWE-863 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N

References

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