CVE-2017-7652 in Mosquitto
Summary
by MITRE
In Eclipse Mosquitto 1.4.14, if a Mosquitto instance is set running with a configuration file, then sending a HUP signal to server triggers the configuration to be reloaded from disk. If there are lots of clients connected so that there are no more file descriptors/sockets available (default limit typically 1024 file descriptors on Linux), then opening the configuration file will fail.
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Analysis
by VulDB Data Team • 03/07/2023
The vulnerability described in CVE-2017-7652 affects Eclipse Mosquitto version 1.4.14, a widely used open source message broker implementing the MQTT protocol. This issue represents a denial of service condition that occurs during the dynamic configuration reloading process when the server receives a HUP signal. The flaw is particularly significant because it demonstrates how legitimate administrative functions can be exploited to disrupt service availability, making it a critical concern for systems relying on continuous MQTT communication.
The technical root cause of this vulnerability lies in the configuration reloading mechanism of Mosquitto's process management. When a HUP signal is sent to the running Mosquitto instance, the system attempts to reload the configuration file from disk. However, under conditions where the server has reached its file descriptor limit, typically set to 1024 on Linux systems, the process fails to open the configuration file. This failure occurs because the system has exhausted available file descriptors, which are essential resources for managing network connections and file operations. The flaw manifests when the server attempts to open the configuration file during reload operations, resulting in a cascading failure that can bring the service to a halt.
The operational impact of this vulnerability extends beyond simple service disruption, as it affects the reliability and availability of MQTT-based messaging infrastructure. When a Mosquitto server reaches its file descriptor limit due to numerous connected clients, administrators face a critical operational challenge where legitimate configuration management activities become impossible. This creates a scenario where the system cannot be properly maintained or updated, potentially leaving security vulnerabilities unaddressed while simultaneously failing to provide the necessary service availability. The vulnerability affects any environment where Mosquitto servers operate with high connection loads, particularly in IoT deployments, industrial automation systems, or any application requiring persistent MQTT connections.
This vulnerability aligns with CWE-400, which categorizes improper handling of resource exhaustion conditions, and demonstrates the importance of proper resource management in server applications. The flaw also relates to ATT&CK technique T1499.004, which covers network denial of service attacks, as the vulnerability can be exploited to disrupt service availability. Organizations implementing MQTT-based solutions should consider implementing proper connection limiting, monitoring file descriptor usage, and establishing robust failover mechanisms. The recommended mitigations include increasing file descriptor limits, implementing proper connection management policies, and ensuring that configuration reload operations are resilient to resource exhaustion scenarios. Additionally, administrators should regularly monitor system resource usage and implement automated alerts to prevent the system from reaching critical resource exhaustion states that could trigger this vulnerability.