CVE-2026-42209

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.

• CWE-369

• https://github.com/halfgaar/FlashMQ/commit/193b6e7767889511cfa8e933908ea5e6a1077a1f
• https://github.com/halfgaar/FlashMQ/issues/167
• https://github.com/halfgaar/FlashMQ/releases/tag/v1.26.1
• https://github.com/halfgaar/FlashMQ/security/advisories/GHSA-2789-vfcg-5922
• https://github.com/halfgaar/FlashMQ/issues/167

Published

May 8, 2026

Last Modified

Jun 17, 2026

Status

Deferred

• How Strix found a critical auth bypass in etcdStrix autonomously discovered a critical authentication bypass in etcd, later designated CVE-2026-33413.
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