RabbitMQ CVE-2026-66067

Exploitation requires three concrete preconditions stated in the advisory: (1) the rabbitmq_stream plugin must be enabled and listening (default stream port 5552); (2) the attacker must possess valid authenticated stream-protocol credentials (PR:L - this is not unauthenticated); and (3) the operator must be relying on per-user and/or per-vhost connection limits as a tenant-isolation control, since the vulnerability only matters where those caps are the enforcement mechanism being bypassed. Limiting factors: authentication is mandatory, impact is confined to availability/resource-exhaustion (no data disclosure or modification), and deployments that neither enable the stream plugin nor depend on connection caps are unaffected. Attack has no user-interaction requirement.

This is a genuine but bounded issue best characterized as a security-control bypass with availability consequences, not a critical breach. The CVSS 4.0 vector (AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N, base 6.0) is internally consistent with the description: network-reachable, low complexity, but requiring valid stream-protocol credentials (PR:L) and yielding availability-only impact (VA:H) with no confidentiality or integrity effect and no scope change. The AT:P (attack requirement) reflects the meaningful preconditions - the rabbitmq_stream plugin must be enabled and the operator must actually rely on per-user/per-vhost connection caps for tenant isolation. No EPSS score, KEV listing, or POC was provided, so exploitation likelihood cannot be quantified from the input; there is no public exploit identified at time of analysis. The affected-versions and fix data are well corroborated (vendor GHSA advisory plus 4.2.7 and 4.3.1 release tags), so patch guidance is high-confidence. Net: real priority only for multi-tenant RabbitMQ operators using the stream plugin and connection limits as an isolation boundary; for single-tenant deployments or those not enforcing connection caps, real-world risk is low. The 'Denial Of Service' tag is accurate to the availability impact.

An authenticated tenant in a shared RabbitMQ cluster, holding valid stream-protocol credentials, opens connections via the stream port 5552 instead of AMQP port 5672. Because the stream open handler only calls check_vhost_access and skips the node/vhost/user connection-limit checks that rabbit_reader enforces for AMQP, the tenant opens far more connections than the operator-configured caps allow, exhausting connection resources and defeating tenant isolation. No public exploit is identified at time of analysis, but the flaw is trivially reproducible given credentials.