# CVE-2026-58209: NATS Server: MQTT retained and QoS replay bypass subscribe deny filters

CVE-2026-58209 is fixed in nats-server on 1 platform by DEBIAN-CVE-2026-58209 (version 2.14.3-1), released July 6, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-58209
- Priority: Routine
- CVSS: 4.3 (Moderate)
- EPSS: 0.0034
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jul 8, 2026
- Weakness: Incorrect Authorization
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-58209

## 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, MQTT retained message delivery and QoS1+ durable replay could deliver messages whose original topics matched a subscriber configured subscribe deny rule because these delivery paths did not consistently recheck the concrete original topic before sending the MQTT PUBLISH to the subscriber. This issue is fixed in versions 2.14.3 and 2.12.12.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | nats-server Debian 14 | 2.14.3-1 | [DEBIAN-CVE-2026-58209](https://patchblox.com/security/data/fix/linux/debian-cve-2026-58209.md) | Jul 6, 2026 |

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Data as of 2026-11-08T13:06:02Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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