Bug 2498259 (CVE-2026-58209)

Summary: CVE-2026-58209 nats-server: NATS Server: Information disclosure due to inconsistent MQTT topic rechecking
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in NATS Server. This vulnerability allows for unauthorized information disclosure where MQTT messages, intended to be denied based on subscription rules, are still delivered to subscribers. This occurs because the server's delivery paths do not consistently recheck the original topic against deny rules before sending the messages, potentially exposing sensitive data to unintended recipients.
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Description OSIDB Bzimport 2026-07-08 21:02:36 UTC
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.