Cyber Resilience

CVE-2026-42209

Medium

Published: 08 May 2026

Published
08 May 2026
Modified
13 May 2026
KEV Added
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Patch
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CVSS Score v3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
EPSS Score 0.0013 32.5th percentile
Risk Priority 13 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2026-42209 is a medium-severity Divide By Zero (CWE-369) vulnerability. Its CVSS base score is 6.5 (Medium).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 32.5th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

EU & UK References

Vulnerability details

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.…

more

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(s)
CWE-369

Related Threats

MITRE ATT&CK Enterprise TechniquesAI

T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
T1499.004 Application or System Exploitation Impact
Adversaries may exploit software vulnerabilities that can cause an application or system to crash and deny availability to users.
attack.mitre.org →
Why these techniques?

Remote exploitation of public-facing MQTT broker leading to application crash via divide-by-zero (CWE-369) directly enables T1190 for initial access and T1499.004 for endpoint DoS.

Confidence: HIGH · MITRE ATT&CK Enterprise v18.1

Affected Assets

Mitigating Controls

No mitigating controls mapped yet. The per-CVE control annotator has not reached this CVE.

References