What’s Vulnerable › Vulnerabilities
CVE-2026-58211: NATS Server: `no_auth_user` pre-CONNECT fast path bypasses user connection restrictions
- Severity: medium (CVSS 5.4 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.3% probability of exploitation in the next 30 days
- Public exploit or detection template: none known
- Published: 2026-07-08 · updated 2026-10-25
- Weakness: CWE-863
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 products
- nats-io nats-server: from 2.12.0 before 2.12.12; from 2.14.0 before 2.14.3 — fixed in 2.12.12, 2.14.3
How to fix
Upgrade to a fixed version: nats-io nats-server 2.12.12, 2.14.3. Check the vendor advisory for mitigations.
References
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