CVE-2026-8686 - Heap out-of-bounds read in coreMQTT MQTT5 property parsing

unknownCVE-2026-8686

Bulletin ID: 2026-032-AWS Scope: AWS Content Type: Important (requires attention) Publication Date: 05/15/2026 11:45 AM PDT Description: coreMQTT is a lightweight MQTT client library for embedded devices. We identified CVE-2026-8686, an issue where missing bounds validation in the MQTT v5.0 SUBACK and UNSUBACK property parser in coreMQTT before 5.0.1 allows an MQTT broker to cause a denial of service (crash via heap out-of-bounds read) by sending a crafted packet. Impacted versions: v5.0.0 Please refer to the article below for the most up-to-date and complete information related to this AWS Security Bulletin.

CSIRTS triage

vendor: AWS product: coreMQTT Denial of serviceaffected: v5.0.0

What: Missing bounds validation allows denial of service via crafted MQTT packets.
Who is affected: Users of coreMQTT version 5.0.0.
Urgency: Remediation is urgent due to the potential for service crashes.
Action: Upgrade to version 5.0.1 or later.

AI-assisted analysis generated from the source advisory — verify against the original.

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Details

Source: AWS Security Bulletins (INTL · vendor-psirt · site)
Severity: unknown
Published: 2026-06-05
Exploitation: Not in CISA KEV at last sync

Original advisory: https://aws.amazon.com/security/security-bulletins/rss/2026-032-aws/

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-86860.39% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 31% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-8686	coverage & exploitation status	NVD · CVE.org

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