# CVE-2026-115417: AWS aws-c-mqtt memory exhaustion in MQTT 3.1.1 adapter

Source: https://junglewise.ai/threats/cve-2026-115417-memory-allocation-with-excessive-size-value-in-the-mqtt-3-1-1  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-22. Updated: 2026-10-22  
License: CC BY 4.0 with a link back

CVE-2026-115417 · Severity: high · CVSS 7.5 · Published 2026-10-22

AWS aws-c-mqtt is a C library that implements MQTT protocol support for IoT devices and applications. An attacker on the network can send specially crafted MQTT messages that cause the client process to attempt to allocate an excessively large amount of memory, leading to a denial of service and application crash. Affected devices and applications using vulnerable versions cannot reconnect to MQTT brokers until restarted.

Technologies: [Amazon AWS](https://junglewise.ai/threats/technologies/aws). Vendors: [Amazon](https://junglewise.ai/threats/vendors/amazon), [AWS](https://junglewise.ai/threats/vendors/aws).

## Quick answers

**Is CVE-2026-115417 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-115417 being exploited in the wild.

**How severe is CVE-2026-115417?** High severity, with a CVSS score of 7.5, published 22 October 2026.

**Which products and versions are affected?** AWS IoT Device SDK for C++ affected versions bundling vulnerable aws-c-mqtt; Aws-C-Mqtt 0.9.1 to 0.16.1.

**Is there a fix for CVE-2026-115417?** Yes: fixed in aws-c-mqtt 0.16.2. Until then: Connect only to trusted MQTT brokers such as AWS IoT Core, which enforces negotiated maximum packet sizes. Use TLS to prevent on-path tampering of broker responses. Where feasible, avoid the MQTT 3.1.1 compatibility adapter and use native MQTT5 client support instead. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-115417 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-115417?** Check whether you run Amazon AWS, AWS IoT Device SDK for C++ or Aws-C-Mqtt at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in aws-c-mqtt 0.16.2

Connect only to trusted MQTT brokers such as AWS IoT Core, which enforces negotiated maximum packet sizes. Use TLS to prevent on-path tampering of broker responses. Where feasible, avoid the MQTT 3.1.1 compatibility adapter and use native MQTT5 client support instead.

## Technical details

A memory allocation vulnerability (CWE-789) exists in the MQTT 3.1.1 compatibility adapter of aws-c-mqtt versions 0.9.1 through 0.16.1 that allows a remote attacker to trigger excessive memory allocation. The vulnerability is triggered by a malicious MQTT broker or on-path attacker during the handshake phase. A fixed version is available (0.16.2).

## Affected products

- AWS aws-c-mqtt 0.9.1 to 0.16.1
- AWS AWS IoT Device SDK for C++ affected versions bundling vulnerable aws-c-mqtt

## Timeline

- 2026-10-22: disclosed

## References

- [https://aws.amazon.com/security/security-bulletins/rss/2026-147-aws/](https://aws.amazon.com/security/security-bulletins/rss/2026-147-aws/)

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