---
id: "GHSA-g3x5-86mr-65p5"
kind: "vulnerability"
aliases: ["GHSA-g3x5-86mr-65p5"]
title: "CVE-2026-115417 - Memory allocation with excessive size value in the MQTT 3.1.1 compatibility adapter in aws-c-mqtt"
severity: "medium"
cvss: null
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["aws", "c++", "embedded", "iot", "lab-disclosure", "mqtt", "package"]
not_affected_if: ["no-mqtt-3.1.1-adapter", "version-fixed"]
published_at: "2026-10-22T00:00:00+00:00"
first_seen_at: "2026-10-24T20:05:36+00:00"
updated_at: "2026-10-25T05:00:39+00:00"
sources: [{"source": "lab", "url": "https://aws.amazon.com/security/security-bulletins/rss/2026-147-aws/", "first_seen_at": "2026-10-24T20:05:36+00:00"}]
---

# CVE-2026-115417 - Memory allocation with excessive size value in the MQTT 3.1.1 compatibility adapter in aws-c-mqtt

The MQTT 3.1.1 compatibility adapter in aws-c-mqtt, the C library in the AWS Common Runtime and AWS IoT Device SDK for C++ v2, allocates memory using an excessive size value (CWE-789). A remote actor can exploit this to cause a denial of service of the client process.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the aws-c-mqtt version in your build or lockfile; affected versions are `>= 0.9.1` and `< 0.16.2`.
- Check whether the AWS IoT Device SDK for C++ v2 is bundled in your application, since it ships aws-c-mqtt.
- Check whether your code uses the MQTT 3.1.1 compatibility adapter rather than a native MQTT5 client.

## Fix

- Upgrade aws-c-mqtt to `v0.16.2` or later.
- Rebuild and redeploy applications that bundle the AWS IoT Device SDK for C++ v2 or any forked copy of aws-c-mqtt.
- Until upgraded, connect only to trusted MQTT brokers such as AWS IoT Core and use TLS.

## Timeline

- 2026-10-24T20:05:36+00:00 lab https://aws.amazon.com/security/security-bulletins/rss/2026-147-aws/ — AWS: CVE-2026-115417 - Memory allocation with excessive size value in the MQTT 3.1.1 compatibility adapter in aws-c-mqtt

## Documents

- [advisory] AWS: CVE-2026-115417 - Memory allocation with excessive size value in the MQTT 3.1.1 compatibility adapter in aws-c-mqtt https://aws.amazon.com/security/security-bulletins/rss/2026-147-aws/

## From the sources

CVE-2026-115417 - Memory allocation with excessive size value in the MQTT 3.1.1 compatibility adapter in aws-c-mqtt

### CVE-2026-115417 - Memory allocation with excessive size value in the MQTT 3.1.1 compatibility adapter in aws-c-mqtt

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.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_