# CVE-2021-34434: Missing authorization in Eclipse Mosquitto

> Attackers can retain unauthorized MQTT subscriptions when using the dynamic security plugin with offline durable clients, bypassing access controls.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 30 Aug 2021
- **Updated:** 4 Aug 2024
- **Also known as:** DEBIAN-CVE-2021-34434, GHSA-cj6r-mprf-8cq9, MGASA-2021-0445, UBUNTU-CVE-2021-34434

## What is CVE-2021-34434?

CVE-2021-34434 is a medium-severity missing authorization vulnerability in Fedoraproject Fedora, published on 30 Aug 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In Eclipse Mosquitto versions 2.0 to 2.0.11, when using the dynamic security plugin, if the ability for a client to make subscriptions on a topic is revoked when a durable client is offline, then existing subscriptions for that client are not revoked.

Weakness: CWE-863 (Incorrect Authorization), CWE-285 (Improper Authorization)

## Which versions are affected by CVE-2021-34434?

It affects 2 products.


Products: Eclipse Mosquitto, Fedoraproject Fedora.

## How do I fix CVE-2021-34434?

Upgrade to a fixed version.

## Is CVE-2021-34434 being exploited?

There is no known exploitation of CVE-2021-34434 in the wild and no public exploit code.

## Other vulnerabilities in Fedoraproject Fedora

- [CVE-2018-12550](https://insights.sbomify.com/CVE-2018-12550/): Auth bypass in Eclipse Mosquitto (high 8.1)
- [CVE-2018-12551](https://insights.sbomify.com/CVE-2018-12551/): Auth bypass in Eclipse Mosquitto (high 8.1)
- [CVE-2023-5632](https://insights.sbomify.com/CVE-2023-5632/): Unconditionally adding an event to the epoll causes excessive CPU consumption (high 7.5)
- [CVE-2023-28366](https://insights.sbomify.com/CVE-2023-28366/): Denial of service in n/a (high 7.5)
- [CVE-2021-41039](https://insights.sbomify.com/CVE-2021-41039/): Denial of service in Eclipse Mosquitto (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-34434 and fix it if it is affected.

What it is: CVE-2021-34434 is a medium-severity missing authorization vulnerability in Fedoraproject Fedora, published on 30 Aug 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-34434 in the wild and no public exploit code.

Affected product: Fedoraproject Fedora. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2021-34434/ (Markdown: https://insights.sbomify.com/CVE-2021-34434/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-34434
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-34434
- OSV: https://osv.dev/vulnerability/CVE-2021-34434

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-34434/
Summaries are generated and may contain mistakes; the official description above is the record.