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DoS from MQTT v5.0 deserialization fault in coreMQTT

High
AniruddhaKanhere published GHSA-6qh9-r6jp-2wxc May 15, 2026

Package

coreMQTT

Affected versions

v5.0.0

Patched versions

v5.0.1

Description

Summary

coreMQTT is a client implementation of the MQTT standard written in C. An issue exists where, under certain circumstances, an MQTT v5.0 broker can trigger a heap out-of-bounds read by sending a crafted SUBACK or UNSUBACK packet.

Impact

This can result in information disclosure (reading adjacent heap memory) or denial of service (crash via out-of-bounds access). This issue can be leveraged via network and requires no authentication.

Impacted versions: v5.0.0

Patches

This issue has been addressed in coreMQTT version 5.0.1. We recommend upgrading to the latest version and ensuring any forked or derivative code is patched to incorporate the new fixes.

Workarounds

There is no workaround for this issue. Upgrade to version 5.0.1 or later.

References

If you have any questions or comments about this advisory, we ask that you contact AWS Security via our vulnerability reporting page or directly via email to aws-security@amazon.com. Please do not create a public GitHub issue.

Acknowledgement

We would like to thank Eun0us of Espilon for collaborating on this issue through the coordinated vulnerability disclosure process.

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVE ID

CVE-2026-8686

Weaknesses

No CWEs

Credits