CVE-2026-42209 MEDIUM

CVE-2026-42209: FlashMQ: Division by zero crash when using non-default deferred retained message setting

Vendor Halfgaar
Product FlashMQ
Weakness CWE-369
Published May 8, 2026
Last update May 11, 2026
View on NVD All CVEs

CVSS base score

6.5/10
Attack vector Network
Attack complexity Low
Privileges required Low
User interaction None
Confidentiality None
Integrity None

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

What the vulnerability does

01Description

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.

Key dates

02Disclosure timeline

May 8, 2026 CVE published
May 11, 2026 Record updated