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VulnerabilityPublished Updated

CVE-2026-42209: halfgaar FlashMQ · Divide By Zero

Affects halfgaar FlashMQSource CVE Database V5

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Not known to be exploited · CVSS 6.5 Medium : upgrade to 1.26.1 when convenient.

Data as of 30 Oct 2026, 06:59 UTC

CVSS 3.1 base score
6.5Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.4% chance of exploitation in 30 days – higher than 37% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 1.26.1
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 8 May 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.

What to do

Upgrade FlashMQ and halfgaar/FlashMQ to 1.26.1.

Affected software

ProductAffectedFixed in
halfgaarFlashMQAffected
  • <1.26.1
Fixed in
  • 1.26.1
GitHubhalfgaar/FlashMQpkg:github/halfgaar/FlashMQOther threatsAffected
  • <1.26.1
Fixed in
  • 1.26.1

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A fix is available in FlashMQ version 1.26.1. Users should upgrade to this version or later to remediate the vulnerability. No other official mitigations or temporary fixes are documented. Patch status is confirmed by the vendor advisory stating the issue is fixed in 1.26.1.

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.

References

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