# CVE-2026-58213: NATS Server protocol injection via MQTT subscription filters

Source: https://junglewise.ai/threats/cve-2026-58213-nats-server-protocol-injection-via-mqtt-subscription-filters  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-08. Updated: 2026-07-08  
License: CC BY 4.0 with a link back

CVE-2026-58213 · Severity: high · CVSS 7.1 · Published 2026-07-08

NATS Server is a high-performance messaging system used for cloud and edge computing. A vulnerability in how the server handles MQTT client requests could allow a user to send specially crafted messages that disrupt the internal communication between servers. This could lead to unauthorized protocol operations or data stream corruption, potentially impacting the integrity and confidentiality of the messaging network.

## Quick answers

**Is CVE-2026-58213 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-58213 being exploited in the wild.

**How severe is CVE-2026-58213?** High severity, with a CVSS score of 7.1, published 8 July 2026.

**Which products and versions are affected?** nats-io NATS Server < 2.12.9, >= 2.14.0-RC.1, < 2.14.1.

**Is there a fix for CVE-2026-58213?** A patch was published on 2026-05-20: Release of versions 2.12.9 and 2.14.1 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-58213 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-58213?** Check whether anything you run is named in the advisory. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

NATS Server is vulnerable to a protocol injection flaw (CWE-74) when handling MQTT subscription filters. An authenticated MQTT client can include protocol control characters in subscription filters or publication subjects. When the server forwards this data to route or leafnode connections, it fails to properly neutralize these characters, leading to the corruption of the NATS protocol stream. This allows an attacker to inject unintended NATS protocol operations into the downstream connection. The issue is resolved in NATS Server versions 2.14.1 and 2.12.9 by ensuring invalid subject characters are rejected during the MQTT ingress process.

## Affected products

- nats-io NATS Server < 2.12.9, >= 2.14.0-RC.1, < 2.14.1

## Timeline

- 2026-07-08: advisory: NVD publication date
- 2026-05-20: patched: Release of versions 2.12.9 and 2.14.1

## References

- [https://github.com/nats-io/nats-server/commit/366837cfc65ab9ccb4f98193c65e8daf238582d8](https://github.com/nats-io/nats-server/commit/366837cfc65ab9ccb4f98193c65e8daf238582d8)
- [https://github.com/nats-io/nats-server/commit/64ebae40051ee497c481e10f316238faf0de1736](https://github.com/nats-io/nats-server/commit/64ebae40051ee497c481e10f316238faf0de1736)
- [https://github.com/nats-io/nats-server/commit/f14856b9e57a36818f43851cb69b6e33670885c9](https://github.com/nats-io/nats-server/commit/f14856b9e57a36818f43851cb69b6e33670885c9)
- [https://github.com/nats-io/nats-server/pull/8163](https://github.com/nats-io/nats-server/pull/8163)
- [https://github.com/nats-io/nats-server/pull/8164](https://github.com/nats-io/nats-server/pull/8164)
- [https://github.com/nats-io/nats-server/releases/tag/v2.12.9](https://github.com/nats-io/nats-server/releases/tag/v2.12.9)
- [https://github.com/nats-io/nats-server/releases/tag/v2.14.1](https://github.com/nats-io/nats-server/releases/tag/v2.14.1)