# CVE-2021-41036: Memory corruption in Eclipse Paho MQTT C Client

> A buffer overflow in the Eclipse Paho MQTT C Client allows attackers to execute arbitrary code or cause denial of service via malformed packets.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/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:** No
- **Published:** 2 Nov 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-m9hg-v7xv-429h, UBUNTU-CVE-2021-41036

## What is CVE-2021-41036?

CVE-2021-41036 is a critical memory corruption vulnerability in The Eclipse Foundation Eclipse Paho MQTT C Client, published on 2 Nov 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In versions prior to 1.1 of the Eclipse Paho MQTT C Client, the client does not check rem_len size in readpacket.

Weakness: CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2021-41036?

It affects 1 product.


Products: Eclipse Paho Mqtt C\/C\+\+ Client.

## How do I fix CVE-2021-41036?

No fix has been published for CVE-2021-41036 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-41036 being exploited?

There is no known exploitation of CVE-2021-41036 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-41036 and fix it if it is affected.

What it is: CVE-2021-41036 is a critical memory corruption vulnerability in The Eclipse Foundation Eclipse Paho MQTT C Client, published on 2 Nov 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-2021-41036 in the wild and no public exploit code.

Affected product: The Eclipse Foundation Eclipse Paho MQTT C Client. 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-2021-41036/ (Markdown: https://insights.sbomify.com/CVE-2021-41036/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-41036
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-41036
- OSV: https://osv.dev/vulnerability/CVE-2021-41036

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From sbomify Insights: https://insights.sbomify.com/CVE-2021-41036/
Summaries are generated and may contain mistakes; the official description above is the record.