# CVE-2018-12551: Auth bypass in Eclipse Mosquitto

> Attackers can bypass authentication in Eclipse Mosquitto by exploiting malformed password file entries, gaining unauthorized access to the broker.

- **Severity:** High 8.1 (`CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 27 Mar 2019
- **Updated:** 5 Aug 2024
- **Also known as:** ALPINE-CVE-2018-12551, DEBIAN-CVE-2018-12551, GHSA-5hh6-jrm5-mqxq, UBUNTU-CVE-2018-12551

## What is CVE-2018-12551?

CVE-2018-12551 is a high-severity authentication bypass vulnerability in The Eclipse Foundation Eclipse Mosquitto, published on 27 Mar 2019. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

When Eclipse Mosquitto version 1.0 to 1.5.5 (inclusive) is configured to use a password file for authentication, any malformed data in the password file will be treated as valid. This typically means that the malformed data becomes a username and no password. If this occurs, clients can circumvent authentication and get access to the broker by using the malformed username. In particular, a blank line will be treated as a valid empty username. Other security measures are unaffected. Users who have only used the mosquitto_passwd utility to create and modify their password files are unaffected by this vulnerability.

Weakness: CWE-287 (Improper Authentication), CWE-703 (Improper Check or Handling of Exceptional Conditions)

## Which versions are affected by CVE-2018-12551?

It affects 1 product.


Products: Eclipse Mosquitto.

## How do I fix CVE-2018-12551?

Apply the vendor's patch.

## Is CVE-2018-12551 being exploited?

There is no known exploitation of CVE-2018-12551 in the wild and no public exploit code.

## Other vulnerabilities in The Eclipse Foundation Eclipse Mosquitto

- [CVE-2018-12550](https://insights.sbomify.com/CVE-2018-12550/): 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)
- [CVE-2021-34432](https://insights.sbomify.com/CVE-2021-34432/): Denial of service in Eclipse Mosquitto (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2018-12551 and fix it if it is affected.

What it is: CVE-2018-12551 is a high-severity authentication bypass vulnerability in The Eclipse Foundation Eclipse Mosquitto, published on 27 Mar 2019. 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-2018-12551 in the wild and no public exploit code.

Affected product: The Eclipse Foundation Eclipse Mosquitto. 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-2018-12551/ (Markdown: https://insights.sbomify.com/CVE-2018-12551/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2018-12551
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2018-12551
- OSV: https://osv.dev/vulnerability/CVE-2018-12551

---
From sbomify Insights: https://insights.sbomify.com/CVE-2018-12551/
Summaries are generated and may contain mistakes; the official description above is the record.