Critical severity · published May 15, 2026
CVE-2026-8686
DoS from MQTT v5.0 Deserialization Fault in core MQTT
9.1
CVSS
0.4%
EPSS
No
On KEV
Description
Missing bounds validation in the MQTT v5.0 property parser in coreMQTT before 5.0.1 allows an MQTT broker to cause a denial of service by sending a crafted packet.
To remediate this issue, users should upgrade to v5.0.1.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
High
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.4% · higher than 33% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
CO
coreMQTT · FreeRTOS
5.0.0 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-8686
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-8686
Vendor Advisory
https://aws.amazon.com/security/security-bulletins/2026-032-aws/
Release Notes
https://github.com/FreeRTOS/coreMQTT/releases/tag/v5.0.1
Vendor Advisory
https://github.com/FreeRTOS/coreMQTT/security/advisories/GHSA-6qh9-r6jp-2wxc