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.

Routine

CVSS

4.3

Moderate

Exploitation

None reported

No vendor assessment

CISA KEV

Not listed

Not in the Known Exploited Vulnerabilities catalog

EPSS

0.0034

27th percentile

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

Product	Fixed in	Fix	Released
Linux
nats-server · Debian 14	2.14.3-1	DEBIAN-CVE-2026-58209	Jul 6, 2026

Details

Published
July 8, 2026
Weakness
Incorrect Authorization
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
Vendor advisory
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-58209

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