CVE-2017-7653 in Mosquitto
Summary
by MITRE
The Eclipse Mosquitto broker up to version 1.4.15 does not reject strings that are not valid UTF-8. A malicious client could cause other clients that do reject invalid UTF-8 strings to disconnect themselves from the broker by sending a topic string which is not valid UTF-8, and so cause a denial of service for the clients.
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Analysis
by VulDB Data Team • 03/21/2023
The Eclipse Mosquitto broker represents a widely deployed open-source message broker implementation that facilitates communication in mqtt-based IoT and messaging systems. This vulnerability affects versions up to 1.4.15 and stems from an insufficient validation mechanism for topic strings. The flaw lies in the broker's failure to properly reject non-UTF-8 compliant strings during message processing, creating a potential vector for malicious exploitation. The vulnerability specifically targets the broker's handling of topic names and payload data that do not conform to valid utf-8 encoding standards.
The technical implementation of this vulnerability occurs at the protocol parsing layer where the broker accepts incoming messages without proper validation of utf-8 compliance. When a malicious client sends topic strings containing invalid utf-8 sequences, the broker processes these inputs without rejection, subsequently propagating them to connected clients. The affected clients that enforce strict utf-8 validation will detect these malformed strings and disconnect from the broker as a protective measure. This cascading effect creates a denial of service condition where legitimate clients are inadvertently disconnected from the messaging infrastructure.
The operational impact of this vulnerability extends beyond simple service disruption to encompass broader security implications for mqtt-based systems. The attack vector allows an unauthorized client to initiate a denial of service against other connected clients without requiring elevated privileges or authentication. This makes the vulnerability particularly dangerous in environments where multiple clients maintain persistent connections to the same broker. The vulnerability aligns with CWE-180, which addresses the issue of incorrect behavior when handling input data, and represents a classic case of insufficient input validation that enables denial of service attacks.
From an attack perspective, this vulnerability follows patterns consistent with the attack technique described in the MITRE ATT&CK framework under T1499, which covers network denial of service attacks. The malicious actor requires only the ability to connect to the broker and send specially crafted messages to trigger the vulnerability. The attack can be executed with minimal resources and provides significant impact in terms of service disruption. Organizations using Mosquitto brokers in production environments face potential operational downtime and service degradation when this vulnerability is exploited.
Mitigation strategies should focus on immediate software updates to versions beyond 1.4.15 where the vulnerability has been addressed through proper utf-8 validation implementation. Network-level defenses such as access control lists and client authentication can provide additional protection layers, though these do not directly address the core validation issue. The broker configuration should include enhanced input validation rules that enforce proper utf-8 encoding for all topic strings and payload data. Organizations should also implement monitoring systems to detect unusual disconnection patterns that may indicate exploitation attempts. Security teams must ensure that all mqtt clients in the ecosystem maintain consistent utf-8 validation practices to prevent cascading failures when interacting with vulnerable brokers.