CVE-2026-42209: halfgaar FlashMQ · Divide By Zero
Affects halfgaar FlashMQSource CVE Database V5
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
- 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:HExploitation evidence
Disclosed: evidence found.
CVE published 8 May 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by 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
| Product | Affected | Fixed in |
|---|---|---|
| halfgaarFlashMQ | Affected
| Fixed in
|
GitHubhalfgaar/FlashMQpkg:github/halfgaar/FlashMQOther threats | Affected
| Fixed in
|
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
- github.com/halfgaar/FlashMQ/security/advisories/GHSA-2789-vfcg-5922 (opens in a new tab)
- github.com/halfgaar/FlashMQ/issues/167 (opens in a new tab)
- github.com/halfgaar/FlashMQ/commit/193b6e7767889511cfa8e933908ea5e6a1077a1f (opens in a new tab)
- github.com/halfgaar/FlashMQ/releases/tag/v1.26.1 (opens in a new tab)