Bug 2498254 (CVE-2026-58208)

Summary: CVE-2026-58208 github.com/nats-io/nats-server: NATS Server: Denial of Service due to incorrect MQTT-over-WebSocket request routing
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
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Priority: medium    
Version: unspecifiedKeywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in NATS Server. An unauthenticated client with access to the WebSocket listener could exploit a vulnerability where requests for the MQTT-over-WebSocket path were incorrectly routed into MQTT handling, even when MQTT was not configured. This allowed the client to access uninitialized MQTT state, leading to a server process crash. This can result in a Denial of Service (DoS) for the NATS Server.
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Bug Depends On: 2499585    
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Description OSIDB Bzimport 2026-07-08 21:02:08 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, a WebSocket listener could route requests for the MQTT-over-WebSocket path into MQTT handling even when MQTT was not configured, allowing an unauthenticated client with access to the WebSocket listener to reach uninitialized MQTT state and crash the server process. This issue is fixed in versions 2.14.3 and 2.12.12.