# CVE-2021-3321: Integer Underflow in Zephyr in IEEE 802154 Fragment Reassembly Header Removal

> An integer underflow in Zephyr RTOS IEEE 802154 fragment reassembly can lead to buffer overflow, potentially allowing code execution or denial of service.

- **Severity:** High 7.5 (`CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 12 Oct 2021
- **Updated:** 16 Sep 2024

## What is CVE-2021-3321?

CVE-2021-3321 is a high-severity vulnerability in Zephyrproject Zephyr, published on 12 Oct 2021. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

Integer Underflow in Zephyr in IEEE 802154 Fragment Reassembly Header Removal. Zephyr versions >= >=2.4.0 contain Integer Overflow to Buffer Overflow (CWE-680). For more information, see https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-w44j-66g7-xw99

Weakness: CWE-191 (Integer Underflow (Wrap or Wraparound)), CWE-680 (Integer Overflow to Buffer Overflow)

## Which versions are affected by CVE-2021-3321?

It affects 1 product.


Products: Zephyrproject Zephyr.

## How do I fix CVE-2021-3321?

No fix has been published for CVE-2021-3321 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-3321 being exploited?

There is no known exploitation of CVE-2021-3321 in the wild and no public exploit code.

## Other vulnerabilities in Zephyrproject Zephyr

- [CVE-2026-5067](https://insights.sbomify.com/CVE-2026-5067/): Out-of-bounds read/write in HTTP WebSocket upgrade via non-null-terminated Sec-WebSocket-Key (critical 9.8)
- [CVE-2022-3806](https://insights.sbomify.com/CVE-2022-3806/): Bluetooth HCI Error Handling Double Free (critical 9.8)
- [CVE-2017-14199](https://insights.sbomify.com/CVE-2017-14199/): Memory corruption in getaddrinfo (critical 9.8)
- [CVE-2018-1000800](https://insights.sbomify.com/CVE-2018-1000800/): Null dereference in n/a (critical 9.8)
- [CVE-2021-3329](https://insights.sbomify.com/CVE-2021-3329/): DOS: Incorrect handling of the initial HCI ACL_MTU handshake packet leads to crash of bluetooth host layer (critical 9.6)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-3321 and fix it if it is affected.

What it is: CVE-2021-3321 is a high-severity vulnerability in Zephyrproject Zephyr, published on 12 Oct 2021. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-3321 in the wild and no public exploit code.

Affected product: Zephyrproject Zephyr. 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-2021-3321/ (Markdown: https://insights.sbomify.com/CVE-2021-3321/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-3321
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-3321
- OSV: https://osv.dev/vulnerability/CVE-2021-3321

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-3321/
Summaries are generated and may contain mistakes; the official description above is the record.