# CVE-2021-21971: Memory corruption in Sealevel

> An attacker can trigger an out-of-bounds write in the URL decoder via a crafted MQTT payload, potentially leading to code execution on the device.

- **Severity:** Low 3.7 (`CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 4 Feb 2022
- **Updated:** 15 Apr 2025
- **Also known as:** GHSA-3975-hvrj-7hm8

## What is CVE-2021-21971?

CVE-2021-21971 is a low-severity memory corruption vulnerability in Sealevel, published on 4 Feb 2022. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

An out-of-bounds write vulnerability exists in the URL_decode functionality of Sealevel Systems, Inc. SeaConnect 370W v1.3.34. A specially-crafted MQTT payload can lead to an out-of-bounds write. An attacker can perform a man-in-the-middle attack to trigger this vulnerability.

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

## Which versions are affected by CVE-2021-21971?

It affects 1 product.


Products: Sealevel Seaconnect 370w Firmware.

## How do I fix CVE-2021-21971?

No fix has been published for CVE-2021-21971 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-21971 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-21971 exists.

## Other vulnerabilities in Sealevel

- [CVE-2021-21960](https://insights.sbomify.com/CVE-2021-21960/): Memory corruption in Sealevel (critical 10.0)
- [CVE-2021-21961](https://insights.sbomify.com/CVE-2021-21961/): Memory corruption in Sealevel (critical 10.0)
- [CVE-2021-21962](https://insights.sbomify.com/CVE-2021-21962/): Memory corruption in Sealevel (critical 9.0)
- [CVE-2021-21964](https://insights.sbomify.com/CVE-2021-21964/): Denial of service in Sealevel (high 8.6)
- [CVE-2021-21965](https://insights.sbomify.com/CVE-2021-21965/): Denial of service in Sealevel (high 8.6)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-21971 and fix it if it is affected.

What it is: CVE-2021-21971 is a low-severity memory corruption vulnerability in Sealevel, published on 4 Feb 2022. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-21971 exists.

Affected product: Sealevel. 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-2021-21971/ (Markdown: https://insights.sbomify.com/CVE-2021-21971/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-21971
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-21971
- OSV: https://osv.dev/vulnerability/CVE-2021-21971

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-21971/
Summaries are generated and may contain mistakes; the official description above is the record.