# CVE-2021-40831: Missing SNI validation and inconsistent CA override function behavior within AWS IoT Device SDKs on Apple devices > Attackers can bypass CA pinning and spoof MQTT brokers on macOS by exploiting missing SNI validation and inconsistent CA override logic in AWS IoT SDKs. - **Severity:** Medium 6.3 (`CVSS:3.1/AV:A/AC:H/PR:H/UI:R/S:U/C:H/I:H/A:H`) - **Exploited in the wild:** Not known - **Login needed:** An administrator - **Attackable:** Local or same network only - **Victim action needed:** A user has to click or open something - **Fix available:** Yes - **Published:** 22 Nov 2021 - **Updated:** 4 Aug 2024 - **Also known as:** GHSA-j3f7-7rmc-6wqj, PYSEC-2021-864 ## What is CVE-2021-40831? CVE-2021-40831 is a medium-severity vulnerability in Amazon Web Services AWS IoT Device SDK v2 for C++, published on 22 Nov 2021. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link. ### Official description The AWS IoT Device SDK v2 for Java, Python, C++ and Node.js appends a user supplied Certificate Authority (CA) to the root CAs instead of overriding it on macOS systems. Additionally, SNI validation is also not enabled when the CA has been “overridden”. TLS handshakes will thus succeed if the peer can be verified either from the user-supplied CA or the system’s default trust-store. Attackers with access to a host’s trust stores or are able to compromise a certificate authority already in the host's trust store (note: the attacker must also be able to spoof DNS in this case) may be able to use this issue to bypass CA pinning. An attacker could then spoof the MQTT broker, and either drop traffic and/or respond with the attacker's data, but they would not be able to forward this data on to the MQTT broker because the attacker would still need the user's private keys to authenticate against the MQTT broker. The 'aws_tls_ctx_options_override_default_trust_store_*' function within the aws-c-io submodule has been updated to address this behavior. This issue affects: Amazon Web Services AWS IoT Device SDK v2 for Java versions prior to 1.5.0 on macOS. Amazon Web Services AWS IoT Device SDK v2 for Python versions prior to 1.7.0 on macOS. Amazon Web Services AWS IoT Device SDK v2 for C++ versions prior to 1.14.0 on macOS. Amazon Web Services AWS IoT Device SDK v2 for Node.js versions prior to 1.6.0 on macOS. Amazon Web Services AWS-C-IO 0.10.7 on macOS. Weakness: CWE-295 (Improper Certificate Validation) ## Which versions are affected by CVE-2021-40831? 7 open source packages ship an affected version, including software.amazon.awssdk.iotdevicesdk:aws-iot-device-sdk, awsiotsdk and aws-iot-device-sdk-v2. It affects 2 products. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `software.amazon.awssdk.iotdevicesdk:aws-iot-device-sdk` | Maven | All versions | 1.5.0 | | `software.amazon.awssdk.iotdevicesdk:aws-iot-device-sdk` | Maven | All versions | 1.5.0 | | `awsiotsdk` | PyPI | All versions | 1.7.0 | | `awsiotsdk` | PyPI | All versions | 1.7.0 | | `awsiotsdk` | PyPI | All versions | 1.7.0 | | `aws-iot-device-sdk-v2` | npm | All versions | 1.6.0 | | `aws-iot-device-sdk-v2` | npm | All versions | 1.6.0 | Products: Amazon Amazon Web Services Aws-C-Io, Amazon Amazon Web Services Internet of Things Device Software Development Kit V2. ## How do I fix CVE-2021-40831? Upgrade software.amazon.awssdk.iotdevicesdk:aws-iot-device-sdk to 1.5.0 or later. ## Is CVE-2021-40831 being exploited? There is no known exploitation of CVE-2021-40831 in the wild and no public exploit code. ## Other vulnerabilities in Amazon Web Services AWS IoT Device SDK v2 for C++ - [CVE-2021-40828](https://insights.sbomify.com/CVE-2021-40828/): TLS hostname validation issues within AWS IoT Device SDKs on Windows (medium 6.3) - [CVE-2021-40830](https://insights.sbomify.com/CVE-2021-40830/): Inconsistent CA override function behavior within AWS IoT Device SDKs on Unix systems (medium 6.3) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2021-40831 and fix it if it is affected. What it is: CVE-2021-40831 is a medium-severity vulnerability in Amazon Web Services AWS IoT Device SDK v2 for C++, published on 22 Nov 2021. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link. Exploitation: There is no known exploitation of CVE-2021-40831 in the wild and no public exploit code. Affected packages and fixed versions: - software.amazon.awssdk.iotdevicesdk:aws-iot-device-sdk (Maven): affected all versions; fixed in 1.5.0 - software.amazon.awssdk.iotdevicesdk:aws-iot-device-sdk (Maven): affected all versions; fixed in 1.5.0 - awsiotsdk (PyPI): affected all versions; fixed in 1.7.0 - awsiotsdk (PyPI): affected all versions; fixed in 1.7.0 - awsiotsdk (PyPI): affected all versions; fixed in 1.7.0 - aws-iot-device-sdk-v2 (npm): affected all versions; fixed in 1.6.0 - aws-iot-device-sdk-v2 (npm): affected all versions; fixed in 1.6.0 Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2021-40831/ (Markdown: https://insights.sbomify.com/CVE-2021-40831/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2021-40831 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-40831 - OSV: https://osv.dev/vulnerability/CVE-2021-40831 --- From sbomify Insights: https://insights.sbomify.com/CVE-2021-40831/ Summaries are generated and may contain mistakes; the official description above is the record.