NATS Server: MQTT retained and QoS replay bypass subscribe deny filters (CVE-2026-58209)
NATS Server versions prior to 2.14.3 and 2.12.12 contain a vulnerability where MQTT retained message delivery and QoS1+ durable replay can bypass subscribe deny filters. This occurs because these delivery paths do not consistently recheck the original topic against deny rules before sending messages to subscribers. The issue allows delivery of messages that should have been blocked by subscription deny rules. A fix is available in versions 2.14.3 and 2.12.12.
AI Analysis
Technical Summary
NATS Server, a messaging system server, has a vulnerability (CVE-2026-58209) affecting MQTT retained message delivery and QoS1+ durable replay mechanisms. In versions prior to 2.14.3 and 2.12.12, these mechanisms can deliver messages whose original topics match a subscriber's configured subscribe deny rule because the system does not consistently recheck the concrete original topic before sending MQTT PUBLISH messages. This results in bypassing subscribe deny filters, potentially allowing unauthorized message delivery. The vulnerability is fixed in versions 2.14.3 and 2.12.12.
Potential Impact
The vulnerability allows messages that should be blocked by subscribe deny rules to be delivered to MQTT subscribers. This could lead to unauthorized message reception, potentially violating access control policies. There are no known exploits in the wild. The severity is assessed as medium.
Mitigation Recommendations
A patch is available and should be applied by upgrading NATS Server to version 2.14.3 or 2.12.12 or later. Users should verify they are running these fixed versions or later to mitigate this issue.
NATS Server: MQTT retained and QoS replay bypass subscribe deny filters (CVE-2026-58209)
Description
NATS Server versions prior to 2.14.3 and 2.12.12 contain a vulnerability where MQTT retained message delivery and QoS1+ durable replay can bypass subscribe deny filters. This occurs because these delivery paths do not consistently recheck the original topic against deny rules before sending messages to subscribers. The issue allows delivery of messages that should have been blocked by subscription deny rules. A fix is available in versions 2.14.3 and 2.12.12.
Affected software
pkg:deb/ubuntu/[email protected]?arch=source&distro=noblepkg:deb/ubuntu/[email protected]?arch=source&distro=questingpkg:deb/ubuntu/[email protected]~esm1?arch=source&distro=esm-apps/resoluteRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
NATS Server, a messaging system server, has a vulnerability (CVE-2026-58209) affecting MQTT retained message delivery and QoS1+ durable replay mechanisms. In versions prior to 2.14.3 and 2.12.12, these mechanisms can deliver messages whose original topics match a subscriber's configured subscribe deny rule because the system does not consistently recheck the concrete original topic before sending MQTT PUBLISH messages. This results in bypassing subscribe deny filters, potentially allowing unauthorized message delivery. The vulnerability is fixed in versions 2.14.3 and 2.12.12.
Potential Impact
The vulnerability allows messages that should be blocked by subscribe deny rules to be delivered to MQTT subscribers. This could lead to unauthorized message reception, potentially violating access control policies. There are no known exploits in the wild. The severity is assessed as medium.
Mitigation Recommendations
A patch is available and should be applied by upgrading NATS Server to version 2.14.3 or 2.12.12 or later. Users should verify they are running these fixed versions or later to mitigate this issue.
Technical Details
- Gcve Source
- db.gcve.eu
- Osv Id
- UBUNTU-CVE-2026-58209
- Osv Schema Version
- 1.7.0
- Ecosystems
- ["Ubuntu:24.04:LTS","Ubuntu:25.10","Ubuntu:Pro:26.04:LTS"]
- Cvss Version
- 3.1
- State
- PUBLISHED
Threat ID: 6a58b46268715ace43d6e7fd
Added to database: 07/16/2026, 10:37:22 UTC
Last enriched: 09/08/2026, 15:20:11 UTC
Last updated: 09/13/2026, 22:01:35 UTC
Views: 32
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