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Vulnerability · Published Jul 8, 2026 · Assigned by GitHub_M

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

Medium 4.3

In plain English

A medium-severity incorrect authorization in nats-server from nats-io. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 28% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)4.3Medium
Exploit odds (30 days)0.3%top 72.1% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

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, 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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Debian:12nats-serverno fix listedDEBIAN-CVE-2026-58209
Debian:13nats-serverno fix listedDEBIAN-CVE-2026-58209
Debian:14nats-server2.14.3-1DEBIAN-CVE-2026-58209
Ubuntu:24.04:LTSnats-serverno fix listedUBUNTU-CVE-2026-58209
Ubuntu:25.10nats-serverno fix listedUBUNTU-CVE-2026-58209
Ubuntu:26.10nats-serverno fix listedUBUNTU-CVE-2026-58209

Affected products (as reported)

VendorProductVersions
nats-io nats-server < 2.12.12>= 2.14.0-RC.1, < 2.14.3

Weakness: CWE-863 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N

References