Bulletin ID: 2026-147-AWS
Scope: AWS
Content Type: Important (requires attention)
Publication Date: 10/22/2026 13:30 PM PDT

Description:

aws-c-mqtt is a C99 implementation of the MQTT 3.1.1 and MQTT5 specifications, distributed as part of the AWS Common Runtime (CRT) and bundled in the AWS IoT Device SDK for C++ v2. We identified CVE-2026-115417, a memory allocation with excessive size value (CWE-789) in the library's MQTT 3.1.1 compatibility adapter. Under certain conditions, a remote actor could cause a denial of service of the client process.

Impacted versions: >= 0.9.1 AND < 0.16.2

Resolution:

This issue has been addressed in aws-c-mqtt version v0.16.2. We recommend upgrading to the latest version and ensuring any forked or derivative code is patched to incorporate the new fixes.

Workarounds:

Connect only to trusted MQTT brokers (for example AWS IoT Core, which enforces the negotiated maximum packet size) and use TLS to prevent on-path tampering of broker responses. Where feasible, avoid the MQTT 3.1.1 compatibility adapter in favor of a native MQTT5 or MQTT 3.1.1 client. Upgrading to a fixed version is the complete remediation.

References:

• CVE-2026-115417
• GHSA-g3x5-86mr-65p5

Acknowledgement:

We would like to thank Eunho Kim for collaborating on this issue through the coordinated vulnerability disclosure process.

Please email aws-security@amazon.com with any security questions or concerns.