CVE-2026-66067: RabbitMQ: Stream protocol skips per vhost per user connection limits

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-09-23 · updated 2026-10-30
Weakness: CWE-770

Description

RabbitMQ is a messaging and streaming broker. Prior to versions 4.2.7 and 4.3.1, The stream open handler calls only check_vhost_access; it omits the node/vhost/user connection-limit checks that rabbit_reader performs for AMQP. A developer %% FIXME comment at the cited line explicitly acknowledges the gap. No compensating enforcement exists in connection tracking or elsewhere in rabbitmq_stream. An authenticated tenant can fully bypass operator-configured per-user and per-vhost connection caps by connecting via port 5552 instead of 5672. Preconditions include rabbitmq_stream plugin enabled Authenticated stream-protocol credentials Operator relies on per-user/per-vhost connection limits for tenant isolation. This issue is fixed in versions 4.2.7 and 4.3.1.

Affected products

rabbitmq-server: from 4.2.0 before 4.2.7; from 4.3.0 before 4.3.1 — fixed in 4.2.7, 4.3.1
rabbitmq-server: from 4.2.0, < 4.2.7; from 4.3.0, < 4.3.1

How to fix

Upgrade to a fixed version: rabbitmq-server 4.2.7, 4.3.1. Check the vendor advisory for mitigations.

References

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