RabbitMQ EUVD-2026-43019

Exploitation requires a specific deployment: the broker must accept traffic through a trusted PROXY-protocol path (proxy_protocol = true) AND the backend AMQP 0-9-1 / AMQP 1.0 / Stream listener must be loopback-bound, so the listener-side socket address reads as 127.0.0.1. The targeted account must be a loopback-restricted user (by default guest, which is in loopback_users) and the attacker must know or default to its credentials (guest/guest out of the box). Limiting factors: brokers not using PROXY protocol, or with listeners bound to routable interfaces, or with the guest/loopback users removed or repermissioned, are not exploitable via this path; no user interaction is needed and no prior authenticated session is required beyond the loopback account's own credentials.

The signals conflict and must be weighed carefully. The published CVSS 3.1 vector (AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H, score 10.0) treats this as a trivial, unauthenticated, network-wide critical - but that rating understates the preconditions: the description explicitly requires a non-default deployment (PROXY protocol accepted over a trusted path AND a loopback-bound backend listener). That is an environmental prerequisite, so real-world attack complexity is higher than AC:L implies. Countervailing signals agree it is not a mass-exploitation event: EPSS is only 0.34% (26th percentile), SSVC marks Automatable=no and Technical Impact=partial, and there is no CISA KEV entry. SSVC does record a proof-of-concept. Net assessment: this is a genuine and serious priority for the specific population of RabbitMQ operators running behind a PROXY-protocol-terminating proxy/load balancer with loopback-bound listeners (a common containerized/HAProxy/Envoy pattern), where a remote attacker can log in as guest/guest and gain full broker access; for the majority of deployments not using that topology it is not remotely reachable. Treat the 10.0 as a worst-case configuration score, not a universal one.

A RabbitMQ cluster runs behind an HAProxy/Envoy load balancer that speaks PROXY protocol to broker listeners bound to 127.0.0.1, with the default guest account still present. A remote attacker on the network connects through the load balancer to the AMQP or Stream port and authenticates as guest/guest; the broker reads the proxy's loopback socket address, treats the session as local, and grants access. The attacker then publishes, consumes, and manipulates messages and queues with guest's permissions. A proof-of-concept is reported per SSVC, and the low attack complexity of the authentication step (default credentials) makes exploitation straightforward once the vulnerable topology is present.