CVE-2026-8686 in coreMQTT
Summary
by MITRE • 05/16/2026
Missing bounds validation in the MQTT v5.0 property parser in coreMQTT before 5.0.1 allows an MQTT broker to cause a denial of service by sending a crafted packet.
To remediate this issue, users should upgrade to v5.0.1.
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Analysis
by VulDB Data Team • 05/21/2026
The vulnerability described represents a critical denial of service weakness in the coreMQTT library's MQTT v5.0 implementation prior to version 5.0.1. This issue stems from inadequate bounds validation within the MQTT property parser component that processes incoming MQTT packets. The flaw specifically affects the protocol's ability to handle malformed property structures that exceed expected buffer limits during packet parsing operations. According to CWE-129, this vulnerability falls under improper validation of array index bounds, which directly enables attackers to exploit memory access violations through crafted malicious payloads. The vulnerability aligns with ATT&CK technique T1499.004, which targets network denial of service conditions by manipulating protocol implementations. The MQTT v5.0 specification defines a complex property structure that includes various data types and lengths, but the parser in affected versions fails to validate these boundaries properly. When an attacker sends a specially crafted MQTT packet containing oversized property values, the parser attempts to process data beyond allocated memory boundaries, leading to memory corruption and ultimately system crash or restart.
The operational impact of this vulnerability extends beyond simple service disruption as it can affect any MQTT broker or client system relying on the vulnerable coreMQTT library. The denial of service condition can be triggered by sending a single malicious packet, making it particularly dangerous in production environments where MQTT brokers handle numerous concurrent connections. Systems utilizing MQTT for critical infrastructure communications, industrial control systems, or IoT deployments face significant risk as this vulnerability can be exploited remotely without authentication requirements. The attack vector requires only that an attacker can establish an MQTT connection to the target system, which is often trivial in networked environments where MQTT brokers are exposed to untrusted networks. Organizations using MQTT-based messaging systems for real-time data exchange, smart grid communications, or automotive systems are particularly vulnerable to cascading failures that could impact operational technology environments.
Mitigation strategies for this vulnerability primarily involve immediate upgrade to coreMQTT version 5.0.1 or later, which implements proper bounds checking in the property parser. This remediation addresses the root cause by ensuring that all property values are validated against expected length constraints before memory allocation occurs. System administrators should also implement network segmentation and access controls to limit exposure of MQTT brokers to untrusted networks, reducing the attack surface for potential exploitation attempts. Additional defensive measures include implementing network monitoring solutions that can detect unusual packet patterns or malformed MQTT traffic, which may indicate exploitation attempts. Organizations should conduct thorough vulnerability assessments of all systems using MQTT implementations to identify potential exposure points and ensure that all components are updated to secure versions. The fix implemented in version 5.0.1 demonstrates proper input validation practices that align with secure coding guidelines and helps prevent similar issues in future implementations. Security teams should also consider implementing automated patch management processes to ensure rapid deployment of security updates across all MQTT-dependent systems and prevent similar vulnerabilities from persisting in operational environments.