CVE-2026-67411 in RabbitMQ
Summary
by MITRE • 09/25/2026
RabbitMQ is a messaging and streaming broker. From 3.13.0 until 3.13.18, 4.0.23, 4.1.14, 4.2.9, and 4.3.3, native MQTT and MQTT over WebSocket behind a trusted PROXY Protocol frontend could lose the proxy-derived client address before the MQTT authentication path checked loopback_users, causing the frontend-to-broker address to be treated as loopback. An attacker who can reach the trusted frontend and has valid credentials for a loopback-restricted account can therefore bypass the source-address restriction; the issue does not bypass password authentication. This issue is fixed in versions 3.13.18, 4.0.23, 4.1.14, 4.2.9, and 4.3.3.
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Analysis
by VulDB Data Team • 09/25/2026
RabbitMQ serves as a robust messaging broker supporting various protocols including MQTT for IoT and real-time data streaming scenarios. In specific versions ranging from RabbitMQ 3.13.0 through 3.13.18, and across the 4.x series up to version 4.3.3, a critical architectural flaw exists within the handling of client connection metadata when operating behind a trusted proxy that utilizes the PROXY Protocol. This configuration is common in cloud-native environments where load balancers or reverse proxies terminate external connections and forward them to backend services while preserving original client IP addresses via protocol-specific headers. The vulnerability arises during the initialization phase of MQTT and MQTT over WebSocket connections, specifically affecting how the broker processes address information derived from these trusted proxy layers before executing security checks related to loopback access policies.
The core technical flaw involves a race condition or ordering error in the authentication pipeline where the original client IP address is prematurely discarded or overwritten by the immediate frontend-to-broker connection address prior to evaluating restrictions on loopback users. Loopback_users are typically configured with strict source-address limitations, allowing such accounts to connect only from localhost addresses like 127.0.0.1 for enhanced security isolation. Because the broker incorrectly treats the proxied connection as originating from a local interface due to this address loss, it erroneously grants access to users designated exclusively for loopback connections. This bypasses the intended network-level restriction without compromising password authentication mechanisms, meaning an attacker who possesses valid credentials for such a restricted account can exploit this misconfiguration to gain unauthorized access from remote networks that should otherwise be blocked by IP-based policies.
From a security impact perspective, this vulnerability allows for privilege escalation through source-address spoofing relative to application-layer permissions rather than network-level isolation. An adversary with knowledge of loopback user credentials and the ability to route traffic through a trusted PROXY Protocol frontend can bypass critical access control lists designed to limit administrative or sensitive operations to local execution contexts. This undermines the defense-in-depth strategy where multiple layers of authentication and authorization are expected to work in concert. The issue is classified under CWE-284, which covers Improper Access Control, specifically relating to misconfiguration issues that allow unauthorized access by bypassing intended restrictions. Furthermore, this behavior aligns with ATT&CK technique T1078, Valid Accounts, as it leverages legitimate credentials but exploits a configuration flaw to achieve access from an unauthorized network location.
Mitigation strategies primarily involve upgrading RabbitMQ to patched versions including 3.13.18, 4.0.23, 4.1.14, 4.2.9, and 4.3.3 where the address handling logic has been corrected to ensure that proxy-derived addresses are properly validated against loopback restrictions before granting access. For environments unable to upgrade immediately, administrators should consider disabling MQTT or WebSocket protocols if they are not strictly required, thereby removing the attack surface entirely. Additionally, implementing strict network segmentation ensures that only authorized proxies can communicate with RabbitMQ instances using PROXY Protocol headers. Monitoring logs for unusual connection patterns from non-loopback sources attempting to authenticate as loopback users may also provide early detection indicators until patches are applied.