Bug 2539787 (CVE-2026-67232)

Summary: CVE-2026-67232 rabbitmq: rabbitmq_web_mqtt: RabbitMQ Web-MQTT plugin: Denial of Service via decompression bomb
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerability-draftAssignee: Product Security DevOps Team <prodsec-dev>
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Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in the `rabbitmq_web_mqtt` plugin of RabbitMQ. An unauthenticated remote attacker can exploit a decompression bomb vulnerability by sending a highly-compressed WebSocket frame. This frame, when decompressed, inflates to gigabytes of memory, leading to a Denial of Service (DoS) by crashing the RabbitMQ node. This occurs during the connection process before any authentication is performed.
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Description OSIDB Bzimport 2026-09-23 20:53:19 UTC 
RabbitMQ is a messaging and streaming broker. Prior to versions 3.13.15, 4.0.20, 4.1.11, 4.2.6, and 4.3.0, The cowboy WebSocket options at line 117 set compress => true, enabling RFC 7692 permessage-deflate negotiation. The handler does not set max_frame_size, so cowboy's default of infinity applies. cowlib's cow_ws:parse_payload/9 calls zlib:inflate/2 on the compressed payload with no output-size limit. An attacker can negotiate permessage-deflate during the WebSocket upgrade and send a frame containing a zlib bomb (e.g. 50 KB → 5 GB). Decompression occurs in the connection process before websocket_handle/2 ever sees the MQTT bytes. An unauthenticated attacker can crash a RabbitMQ node running the Web-MQTT plugin by sending a single highly-compressed WebSocket frame (a few KB on the wire) that inflates to gigabytes in memory. The cowboy WebSocket handler decompresses the entire frame before the MQTT CONNECT packet is processed, so no credentials are required. Preconditions include rabbitmq_web_mqtt plugin enabled (not default, but common for browser clients) Network reachability to port 15675/15676 No authentication required. This issue is fixed in versions 3.13.15, 4.0.20, 4.1.11, 4.2.6, and 4.3.0.