CVE-2018-20145 in Mosquitto
Summary
by MITRE
Eclipse Mosquitto 1.5.x before 1.5.5 allows ACL bypass: if the option per_listener_settings was set to true, and the default listener was in use, and the default listener specified an acl_file, then the acl file was being ignored.
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Analysis
by VulDB Data Team • 06/19/2023
Eclipse Mosquitto represents a widely deployed open-source message broker implementing the MQTT protocol, serving critical infrastructure roles in IoT deployments and industrial automation systems. The vulnerability described in CVE-2018-20145 specifically targets the access control mechanisms within this messaging system, creating a significant security weakness that could allow unauthorized users to bypass authentication and authorization checks. This flaw exists in versions 1.5.x prior to 1.5.5, affecting organizations that rely on Mosquitto for secure message routing and broker management across distributed systems.
The technical root cause of this vulnerability stems from a configuration processing error within the Mosquitto access control list implementation. When administrators configure the per_listener_settings option to true, the system should properly apply access controls for each listener instance. However, the flaw occurs specifically when the default listener is in use and has an acl_file specified, causing the system to ignore the configured access control file entirely. This represents a classic case of improper input validation and configuration handling, where the software fails to properly validate or process the access control settings when multiple listener configurations are present. The vulnerability manifests as a privilege escalation issue where authenticated users can bypass access controls that should restrict their message publishing or subscription capabilities.
The operational impact of this vulnerability extends beyond simple unauthorized access to encompass potential data breaches, service disruption, and system compromise within IoT environments. Organizations using Mosquitto for critical infrastructure monitoring, industrial control systems, or smart city deployments face significant risk when this vulnerability exists, as attackers could potentially publish malicious messages, subscribe to sensitive data streams, or disrupt message flow between components. This bypass allows attackers to gain privileges that should be restricted to specific user roles or client connections, potentially enabling lateral movement within networked systems or data exfiltration from connected IoT devices. The vulnerability particularly affects deployments where multiple listeners are configured but default settings are still in use, creating a dangerous condition where access controls become ineffective.
The flaw aligns with CWE-284, which describes improper access control in software systems, and demonstrates how configuration management issues can create security weaknesses in network services. From an adversarial perspective, this vulnerability maps to ATT&CK technique T1078 for valid accounts and T1566 for spearphishing, as attackers could exploit the bypass to gain unauthorized access to message flows and potentially escalate privileges within the messaging infrastructure. Organizations should implement immediate mitigation strategies including upgrading to Mosquitto version 1.5.5 or later, reviewing all configuration files to ensure proper access control settings, and implementing network segmentation to limit exposure. Additionally, security monitoring should be enhanced to detect unusual message traffic patterns that might indicate unauthorized access attempts, while regular security audits should verify that access control configurations are properly enforced across all listener instances.