CVE-2017-7650 in Mosquitto
Summary
by MITRE
In Mosquitto before 1.4.12, pattern based ACLs can be bypassed by clients that set their username/client id to '#' or '+'. This allows locally or remotely connected clients to access MQTT topics that they do have the rights to. The same issue may be present in third party authentication/access control plugins for Mosquitto.
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Analysis
by VulDB Data Team • 08/23/2024
The vulnerability identified as CVE-2017-7650 represents a critical access control flaw in the Mosquitto MQTT broker software that affects versions prior to 1.4.12. This security issue specifically targets the pattern-based Access Control List (ACL) implementation within the broker, which is designed to enforce authorization rules for MQTT topic access. The flaw stems from improper handling of wildcard characters in client identifiers and usernames, creating a significant bypass mechanism that undermines the intended security posture of the system. Organizations relying on Mosquitto for IoT communications, industrial automation, or any MQTT-based messaging infrastructure face substantial risk from this vulnerability.
The technical root cause of this vulnerability lies in how Mosquitto processes pattern matching for ACL rules when clients use specific wildcard characters in their identifiers. When a client connects to the broker with a username or client identifier containing the '#' or '+' characters, the pattern matching logic fails to properly validate these inputs against the ACL rules. This allows malicious or compromised clients to exploit the ACL system by crafting connection parameters that match multiple topic patterns simultaneously. The '#' wildcard typically represents zero or more topic levels in MQTT, while '+' represents a single topic level, but in this case, their presence in client identifiers creates an unexpected bypass condition. This behavior violates the fundamental principle of least privilege that security systems should enforce, allowing unauthorized access to protected MQTT topics.
The operational impact of this vulnerability extends beyond simple unauthorized access to potentially enabling sophisticated attack scenarios. Locally connected clients can exploit this flaw to gain access to topics they should not be permitted to read or publish to, while remotely connected clients can leverage the same vulnerability to traverse network boundaries and access sensitive data. This issue particularly affects IoT deployments where Mosquitto serves as a messaging backbone for smart devices, industrial sensors, or connected vehicles, where unauthorized access to topic data could lead to data breaches, system compromise, or operational disruption. The vulnerability's presence in third-party authentication plugins compounds the risk, as organizations using custom security extensions may also be affected, creating a broader attack surface that extends beyond the core Mosquitto software.
Organizations should immediately implement mitigation strategies including upgrading to Mosquitto version 1.4.12 or later, which contains the necessary fixes for this vulnerability. The patch addresses the core issue by implementing proper validation of client identifiers during the ACL matching process, ensuring that wildcard characters in usernames and client IDs do not bypass authorization rules. Additionally, administrators should review existing ACL configurations to identify any patterns that might be susceptible to exploitation and implement additional monitoring controls to detect unusual connection patterns. This vulnerability aligns with CWE-284, which describes improper access control, and maps to ATT&CK technique T1078 for valid accounts and T1566 for credential access, emphasizing the need for comprehensive security measures beyond just patching. Organizations should also consider implementing network segmentation, additional authentication layers, and regular security audits to prevent exploitation of similar vulnerabilities in their MQTT-based systems.