CVE-2026-42209
MediumCVSS 6.5Exploitation Probability (EPSS)
Low risk37th percentile - higher than 37% of all known CVEs
Summary
In FlashMQ prior to version 1.26.1, a remote client with retained publish permission can crash the broker when both set_retained_message_defer_timeout and set_retained_message_defer_timeout_spread are configured to non-default values, resulting in denial of service. If anonymous retained publishing is allowed, no authentication is required; otherwise, the attacker needs the corresponding publish permission. The issue is patched in version 1.26.1.
Risk Assessment
This can lead to unavailability of the MQTT broker, disrupting communication for devices and applications relying on FlashMQ. The risk affects environments with non-default retained message defer timeout configuration.
Recommendation
Upgrade FlashMQ to version 1.26.1 or later. Consider disabling anonymous retained publishing and restricting publish permissions to trusted clients.
Other vulnerabilities in FlashMQ
See all- CVE-2026-46411Medium
FlashMQ before version 1.26.2 allows authorized clients to exceed the permitted over-commit of their write buffer, triggering an internal safe-guard exception. This exception is in a path that cannot be caught, causing a server abort.
- CVE-2025-62723Medium
FlashMQ is a MQTT broker/server, designed for multi-CPU environments. Prior to version 1.23.2, any authenticated user can create sessions and have them collect QoS messages. When not sent to a client, these are then not released upon (eventual) session expiration. Version 1.23.2 fixes the issue.
Original NVD description (English source)
FlashMQ is a MQTT broker/server, designed for multi-CPU environments. Prior to version 1.26.1, a remote client with retained publish permission can crash the FlashMQ broker when both set_retained_message_defer_timeout and set_retained_message_defer_timeout_spread are configured to non-default values, resulting in denial of service. If anonymous retained publishing is allowed, no authentication is required; otherwise, the attacker needs the corresponding publish permission. This issue has been patched in version 1.26.1.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS