--- url: "https://www.xcademia.com/news/aws-fixes-cve-2026-115417-mqtt-library-vulnerability-could-disrupt-client-applications" title: "AWS Fixes CVE-2026-115417: MQTT Library Vulnerability Could Disrupt Client Applications" description: "AWS fixes CVE-2026-115417 in aws-c-mqtt. Learn which versions are affected, how the MQTT denial-of-service vulnerability works, and how to patch it." publishedAt: "2026-10-23T10:08:38.025+00:00" updatedAt: "2026-10-23T11:46:10.294473+00:00" type: news category: cybersecurity source_name: Amazon Web Services (AWS) Security Bulletins source_url: "https://aws.amazon.com/security/security-bulletins/2026-147-aws/ " tags: - "#Cybersecurity" - "#AWS" - "#CloudSecurity" - "#IoTSecurity" - "#MQTT" - "#CVE2026115417" - "#VulnerabilityManagement" - "#SoftwareSecurity" --- # AWS Fixes CVE-2026-115417: MQTT Library Vulnerability Could Disrupt Client Applications > AWS has addressed CVE-2026-115417, a vulnerability in the aws-c-mqtt library that could allow remote denial of service in affected MQTT clients. Developers should upgrade to version 0.16.2 and review AWS mitigation guidance. Source: **Amazon Web Services (AWS) Security Bulletins** · 23 October 2026 **A**mazon Web Services (AWS) has disclosed a security vulnerability in `aws-c-mqtt`, a C library used to implement MQTT messaging protocols. Tracked as **CVE-2026-115417**, the issue involves memory allocation with an excessive size value in the library's MQTT 3.1.1 compatibility adapter. Under certain conditions, a remote actor could exploit the issue to cause a denial of service in the client process. AWS has addressed the vulnerability in `aws-c-mqtt` version **v0.16.2** and recommends upgrading to the fixed release. The bulletin was published on October 22, 2026, and is classified as an important security notice requiring attention. Developers maintaining applications that use the affected library should check their dependencies and apply the recommended update. ## What Is CVE-2026-115417? CVE-2026-115417 describes a memory allocation vulnerability in the MQTT 3.1.1 compatibility adapter within `aws-c-mqtt`. The issue is associated with CWE-789, which covers memory allocation using an excessive size value. In general terms, this weakness occurs when software attempts to allocate an unexpectedly large amount of memory based on an input value. Depending on how the application handles that allocation, the result can be excessive resource consumption or disruption of the affected process. AWS states that, under certain conditions, a remote actor could cause a denial of service in the client process. The bulletin does not disclose a specific exploitation sequence, a CVSS severity score, or evidence of active exploitation. ## What Is aws-c-mqtt? `aws-c-mqtt` is a C99 implementation of the MQTT 3.1.1 and MQTT 5 specifications. It is distributed as part of the AWS Common Runtime (CRT) and bundled in the AWS IoT Device SDK for C++ v2. MQTT is a lightweight messaging protocol commonly used in connected-device and Internet of Things (IoT) environments. It enables devices and applications to exchange messages through a broker rather than requiring every participant to communicate directly with every other participant. For example, a connected sensor might publish a temperature reading to an MQTT broker, while another application subscribes to receive that reading. The affected component is specifically the MQTT 3.1.1 compatibility adapter in `aws-c-mqtt`. The advisory does not state that every MQTT implementation or all applications using AWS IoT services are vulnerable. ## Which Versions Are Affected? AWS identifies the affected version range as: - **Affected:** `aws-c-mqtt` versions greater than or equal to `0.9.1` and lower than `0.16.2`. - **Fixed:** `aws-c-mqtt` version `0.16.2`. Applications using a vulnerable version should be reviewed to determine whether they include the affected compatibility adapter. Teams should also check forked or derivative implementations, as AWS explicitly recommends incorporating the fixes into those codebases. ## How Could the Vulnerability Affect Applications? The reported consequence is denial of service against the client process under certain conditions. A denial-of-service issue can interrupt an application's normal operation. For an IoT client, this could potentially affect its ability to continue exchanging messages while the process is disrupted. The practical impact depends on the affected application, how it uses the library, and the conditions under which the vulnerability can be triggered. AWS has not disclosed specific customer incidents, confirmed exploitation in the wild, or quantified the operational impact. Additional details were not disclosed in the announcement. ![CVE-2026-115417](https://0a515t3ure77wbvx.public.blob.vercel-storage.com/articles/1792743561250-cve-2026-115417.webp) ## AWS Recommends Upgrading to Version 0.16.2 AWS identifies version `v0.16.2` as the release containing the fix and recommends upgrading to the latest version. Development teams should prioritize the following actions: **1. Identify affected dependencies** Review project manifests, lockfiles, dependency trees, and build configurations to determine whether the application includes an affected `aws-c-mqtt` version. **2. Upgrade the library** Move to version `v0.16.2` or a later suitable fixed release, following the project's dependency and compatibility requirements. **3. Patch forked or derivative code** If the application uses a fork or modified copy of the library, verify that the security fix has been incorporated. Updating a package in the main dependency manifest may not address a separately maintained copy. **4. Validate the application** After upgrading, run appropriate tests to confirm that MQTT connectivity, message handling, and application recovery behavior continue to work as expected. **5. Review exposure and monitoring** Determine which applications use the affected component and review relevant application logs and operational monitoring for unexpected client-process interruptions. This is a general defensive recommendation, not a mitigation specifically prescribed by AWS. ## Temporary Mitigations Recommended by AWS AWS also outlines several workarounds for teams that cannot immediately complete the upgrade. **Connect only to trusted MQTT brokers** AWS recommends connecting only to trusted MQTT brokers. It gives AWS IoT Core as an example because the service enforces the negotiated maximum packet size. This recommendation can help reduce exposure to untrusted broker responses. It should not be treated as a replacement for upgrading to the fixed library version. **Use TLS** AWS recommends using Transport Layer Security (TLS) to prevent on-path tampering with broker responses. TLS protects communications against certain forms of interception and modification while data travels between endpoints. It does not replace the library update or resolve every possible source of malicious input. **Avoid the compatibility adapter where feasible** AWS advises avoiding the MQTT 3.1.1 compatibility adapter where feasible and using a native MQTT 5 or MQTT 3.1.1 client instead. The suitability of this option depends on the application's implementation and compatibility requirements. Teams should test any client changes before deploying them to production. **AWS states that upgrading to a fixed version is the complete remediation.** Temporary workarounds should therefore be treated as interim risk-reduction measures rather than permanent fixes. ![CVE-2026-115417-remediation-checklist](https://0a515t3ure77wbvx.public.blob.vercel-storage.com/articles/1792743781401-cve-2026-115417-remediation-checklist.webp) ## What Developers and Cloud Security Teams Should Know This bulletin highlights the importance of tracking security issues in software dependencies, including libraries embedded within larger SDKs. Applications may rely on a library indirectly through an SDK or another package. As a result, checking only the application's primary dependencies may not always provide a complete picture of the components included in a build. For engineering teams, the practical response is to establish which applications use the affected component, determine whether a vulnerable version is present, and coordinate the upgrade with application testing. Cloud security teams should also distinguish between a vulnerability in a client-side library and a vulnerability in the cloud service itself. The AWS bulletin identifies the affected component as `aws-c-mqtt`; it does not state that AWS IoT Core itself is vulnerable. The announcement also demonstrates why temporary mitigations and complete remediation need to be tracked separately. Trusted brokers, TLS, and alternative client implementations can help reduce exposure in applicable environments, but AWS identifies the fixed library version as the complete remediation. ![securing-MQTT](https://0a515t3ure77wbvx.public.blob.vercel-storage.com/articles/1792750102540-securing-mqtt.webp) ## Conclusion AWS has addressed CVE-2026-115417 in `aws-c-mqtt`, a memory allocation vulnerability in the MQTT 3.1.1 compatibility adapter that could cause denial of service in the client process under certain conditions. Developers should identify affected dependencies, upgrade to version `v0.16.2` or a later suitable fixed release, and ensure that forked or derivative code incorporates the fix. Where an immediate upgrade is not possible, AWS recommends using trusted MQTT brokers, TLS, and alternative native MQTT clients where feasible. For organizations running IoT applications, the key takeaway is straightforward: verify whether the affected library is present, apply the fixed version, and validate the update across the applications that depend on it. ## Original source https://aws.amazon.com/security/security-bulletins/2026-147-aws/ ## Tags `#Cybersecurity` · `#AWS` · `#CloudSecurity` · `#IoTSecurity` · `#MQTT` · `#CVE2026115417` · `#VulnerabilityManagement` · `#SoftwareSecurity` --- ## About this content This Markdown news article is the citation-grade twin of [AWS Fixes CVE-2026-115417: MQTT Library Vulnerability Could Disrupt Client Applications](https://www.xcademia.com/news/aws-fixes-cve-2026-115417-mqtt-library-vulnerability-could-disrupt-client-applications). It is published by **Xcademia** (UK Companies House 12322710) and is available for AI search engines and large language models to index, summarise, and cite. 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