CVE-2018-12546 in Mosquitto
Summary
by MITRE
In Eclipse Mosquitto version 1.0 to 1.5.5 (inclusive) when a client publishes a retained message to a topic, then has its access to that topic revoked, the retained message will still be published to clients that subscribe to that topic in the future. In some applications this may result in clients being able cause effects that would otherwise not be allowed.
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Analysis
by VulDB Data Team • 05/22/2020
The vulnerability identified as CVE-2018-12546 affects Eclipse Mosquitto versions ranging from 1.0 through 1.5.5, representing a significant access control flaw in message broker implementations. This issue stems from a failure in the retained message handling mechanism within the MQTT protocol implementation, where the system does not properly enforce access restrictions when delivering previously stored messages to new subscribers. The flaw creates a persistent security gap that can be exploited by malicious actors who have previously published retained messages to topics they no longer have access to, thereby undermining the integrity of the access control system.
The technical root cause of this vulnerability lies in the improper state management of retained messages within the broker's memory structures. When a client publishes a retained message to a topic and subsequently loses access to that topic through permission revocation, the broker fails to remove or invalidate the retained message from its storage. This design flaw allows future subscribers to receive messages that were originally published by a client who no longer possesses the appropriate privileges to publish to that topic. The vulnerability manifests as a failure to maintain consistency between access control policies and message delivery mechanisms, creating a scenario where historical message data can be accessed by unauthorized parties.
From an operational perspective, this vulnerability presents a serious risk to systems that rely on strict access controls for sensitive data transmission. The impact extends beyond simple information disclosure to potentially enable privilege escalation or unauthorized data manipulation, depending on the nature of the retained messages and the application's security model. Attackers can exploit this weakness by publishing sensitive retained messages to topics they temporarily control, then revoke their access and observe how those messages are delivered to other legitimate subscribers who should not have access to that information. This behavior violates fundamental security principles and can compromise the confidentiality and integrity of message-based communications.
The vulnerability aligns with CWE-284, which addresses improper access control in software systems, and demonstrates how insufficient access control validation can create persistent security weaknesses. From an ATT&CK framework perspective, this issue relates to privilege escalation and defense evasion techniques, as it allows attackers to maintain access to information that should be restricted. The flaw also intersects with the concept of information exposure, where retained messages become accessible beyond their intended access boundaries. Organizations using affected versions of Eclipse Mosquitto should immediately implement mitigations including upgrading to patched versions, implementing additional access control layers, and conducting thorough security audits of retained message policies to prevent unauthorized information disclosure and maintain the integrity of their MQTT-based communication systems.