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

> Attackers can bypass user connection restrictions by exploiting a parser path when the first operation is not CONNECT, requiring no_auth_user configuration.

- **Severity:** Medium 5.4 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 8 Jul 2026
- **Updated:** 9 Jul 2026
- **Also known as:** DEBIAN-CVE-2026-58211, GHSA-hmmp-q8cx-v964, UBUNTU-CVE-2026-58211

## What is CVE-2026-58211?

CVE-2026-58211 is a medium-severity authentication bypass vulnerability in nats-io nats-server, published on 8 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### 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.

Weakness: CWE-863 (Incorrect Authorization)

## Which versions are affected by CVE-2026-58211?

It affects 1 product.


Products: Linuxfoundation Nats-Server.

## How do I fix CVE-2026-58211?

Upgrade to a fixed version.

## Is CVE-2026-58211 being exploited?

There is no known exploitation of CVE-2026-58211 in the wild and no public exploit code.

## Other vulnerabilities in nats-io nats-server

- [CVE-2022-28357](https://insights.sbomify.com/CVE-2022-28357/): NATS nats-server allows directory traversal via unintended path to a management action (critical 9.8)
- [CVE-2026-58253](https://insights.sbomify.com/CVE-2026-58253/): NATS Server: Route API Auth Bypass (high 8.8)
- [CVE-2022-24450](https://insights.sbomify.com/CVE-2022-24450/): Incorrect Authorization in NATS nats-server (high 8.8)
- [CVE-2026-33216](https://insights.sbomify.com/CVE-2026-33216/): NATS has MQTT plaintext password disclosure (high 8.6)
- [CVE-2026-58207](https://insights.sbomify.com/CVE-2026-58207/): NATS Server: Remote crash via integer overflow in Connz pagination (high 7.7)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-58211 and fix it if it is affected.

What it is: CVE-2026-58211 is a medium-severity authentication bypass vulnerability in nats-io nats-server, published on 8 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-58211 in the wild and no public exploit code.

Affected product: nats-io nats-server. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-58211/ (Markdown: https://insights.sbomify.com/CVE-2026-58211/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-58211
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-58211
- OSV: https://osv.dev/vulnerability/CVE-2026-58211

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-58211/
Summaries are generated and may contain mistakes; the official description above is the record.