Is CVE-2026-42209 in the CISA KEV catalog?

No. CVE-2026-42209 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-42209?

CVE-2026-42209 has a CVSS v3 base score of 6.5 (MEDIUM).

What is the EPSS score for CVE-2026-42209?

CVE-2026-42209 has an EPSS score of 0.36% (28th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix or mitigate CVE-2026-42209?

No published fix for CVE-2026-42209 has been found yet. Check the linked vendor advisories for guidance as it becomes available.

CVE & CISA-KEV Catalog

CVE-2026-42209

MEDIUM

6.5

CVSS v3

NVD

Description

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

How to fix

No published remediation has been found for this vulnerability's affected products yet.

Mitigation guidance may be in the linked vendor advisories in the References section below.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredLow

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityNone

AvailabilityHigh

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

Exploit Intelligence

0.36%probability of exploitation in 30 days

28thpercentile

Low risk: more likely to be exploited than 28% of all known CVEs.

References

Other references4

Embed a live status badge for CVE-2026-42209

Markdown

[![CVE-2026-42209](https://tridentstack.com/cve/badge/CVE-2026-42209.svg)](https://tridentstack.com/cve/CVE-2026-42209)

HTML

<a href="https://tridentstack.com/cve/CVE-2026-42209"><img src="https://tridentstack.com/cve/badge/CVE-2026-42209.svg" alt="CVE-2026-42209"></a>

Find and fix vulnerabilities across your fleet

TridentStack Control continuously scans your Windows, macOS, and Linux fleet for known vulnerabilities, prioritizes them by severity and active exploitation, and patches them automatically.

Start free

This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-05-13.