CVE-2021-28166 in Mosquitto
Summary
by MITRE • 04/08/2021
In Eclipse Mosquitto version 2.0.0 to 2.0.9, if an authenticated client that had connected with MQTT v5 sent a crafted CONNACK message to the broker, a NULL pointer dereference would occur.
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Analysis
by VulDB Data Team • 04/11/2021
The vulnerability CVE-2021-28166 represents a critical NULL pointer dereference flaw within the Eclipse Mosquitto MQTT broker software ecosystem. This issue affects versions 2.0.0 through 2.0.9, making it a significant concern for organizations relying on MQTT protocol implementations for their messaging infrastructure. The vulnerability specifically targets the broker's handling of MQTT v5 protocol connections, where authenticated clients can trigger the flaw through carefully crafted CONNACK messages. From a cybersecurity perspective, this vulnerability falls under the category of denial of service attacks that can potentially disrupt critical messaging services. The flaw demonstrates a classic software engineering oversight where proper input validation and memory management procedures were not adequately implemented in the broker's protocol handling logic. This vulnerability is particularly dangerous because it can be exploited by authenticated clients, meaning that an attacker with valid credentials could potentially disrupt the entire broker service, affecting all connected clients and undermining the reliability of the messaging infrastructure.
The technical execution of this vulnerability occurs when an authenticated MQTT v5 client sends a specially crafted CONNACK message to the broker. The broker fails to properly validate the incoming message structure and subsequently attempts to dereference a NULL pointer during the message processing routine. This NULL pointer dereference results in an immediate crash of the Mosquitto broker process, leading to a complete service disruption. The flaw exists in the protocol implementation layer where the broker does not perform adequate bounds checking or null validation before accessing message fields. According to CWE classification, this vulnerability maps to CWE-476 which specifically addresses NULL pointer dereference conditions in software implementations. The attack vector is relatively straightforward as it requires only an authenticated connection, making it accessible to users with valid credentials who may have legitimate access to the broker. From an operational standpoint, this vulnerability creates a scenario where authorized users can cause significant disruption to services, potentially leading to loss of critical messaging functionality and requiring immediate system restarts to restore normal operations.
The operational impact of CVE-2021-28166 extends beyond simple service disruption to encompass broader security implications for MQTT-based messaging systems. Organizations utilizing Mosquitto brokers in production environments face potential business continuity risks as the vulnerability can be exploited to cause denial of service conditions that may affect real-time communications, IoT device management, and automated system operations. The vulnerability's exploitation does not require advanced technical skills or special privileges beyond valid authentication credentials, making it particularly concerning for environments where multiple users have access to the broker. This flaw can be leveraged in both intentional attacks and accidental system disruptions, as the crafted CONNACK messages could theoretically be generated through misconfigured client applications or automated tools. The impact is particularly severe in IoT deployments where Mosquitto serves as a core messaging component for device communication, potentially leading to cascading failures across connected systems. From an ATT&CK framework perspective, this vulnerability aligns with techniques involving service disruption and system compromise, specifically mapping to T1499 for network disruption and T1566 for social engineering through protocol manipulation.
Organizations should implement immediate mitigations including upgrading to Mosquitto version 2.0.10 or later, which contains the necessary patches to address this vulnerability. The upgrade process should be carefully planned to minimize service disruption while ensuring all broker instances are updated. Additional defensive measures include implementing network segmentation to limit access to MQTT brokers, enforcing strict authentication controls, and monitoring for unusual CONNACK message patterns that may indicate exploitation attempts. Security teams should also consider implementing intrusion detection systems that can identify and alert on malformed MQTT protocol messages. Configuration hardening practices should be applied to restrict unnecessary client capabilities and reduce the attack surface. The vulnerability highlights the importance of proper input validation and memory safety practices in protocol implementations, reinforcing industry best practices established by standards such as the OWASP Top 10 and NIST cybersecurity guidelines. Regular security assessments and vulnerability scanning should be conducted to identify similar issues in other MQTT implementations and ensure comprehensive protection of messaging infrastructure.