# CVE-2025-66647: RIOT OS has buffer overflow in gnrc_ipv6_ext_frag_reass

> Attacker can trigger buffer overflow in IPv6 reassembly to corrupt memory and potentially execute code on IoT devices using RIOT OS.

- **Severity:** Low 1.7 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:U`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 17 Dec 2025
- **Updated:** 17 Dec 2025
- **Also known as:** GHSA-wh3v-q6vr-j79r

## What is CVE-2025-66647?

CVE-2025-66647 is a low-severity memory corruption vulnerability in RIOT-OS RIOT, published on 17 Dec 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

RIOT is an open-source microcontroller operating system, designed to match the requirements of Internet of Things (IoT) devices and other embedded devices. A vulnerability was discovered in the IPv6 fragmentation reassembly implementation of RIOT OS v2025.07. When copying the contents of the first fragment (offset=0) into the reassembly buffer, no size check is performed. It is possible to force the creation of a small reassembly buffer by first sending a shorter fragment (also with offset=0). Overflowing the reassembly buffer corrupts the state of other packet buffers which an attacker might be able to used to achieve further memory corruption (potentially resulting in remote code execution). To trigger the vulnerability, the `gnrc_ipv6_ext_frag` module must be included and the attacker must be able to send arbitrary IPv6 packets to the victim. Version 2025.10 fixes the issue.

Weakness: CWE-120 (Buffer Copy without Checking Size of Input)

## Which versions are affected by CVE-2025-66647?

It affects 1 product.


Products: Riot-Os Riot.

## How do I fix CVE-2025-66647?

No fix has been published for CVE-2025-66647 yet. Limit exposure of the affected software until one is available.

## Is CVE-2025-66647 being exploited?

There is no known exploitation of CVE-2025-66647 in the wild and no public exploit code.

## Other vulnerabilities in RIOT-OS RIOT

- [CVE-2024-32017](https://insights.sbomify.com/CVE-2024-32017/): Buffer overflows in RIOT (critical 9.8)
- [CVE-2023-33975](https://insights.sbomify.com/CVE-2023-33975/): RIOT-OS vulnerable to Out of Bounds Write in _rbuf_add (critical 9.8)
- [CVE-2023-24819](https://insights.sbomify.com/CVE-2023-24819/): RIOT-OS vulnerable to Buffer Overflow during IPHC receive (critical 9.8)
- [CVE-2023-24823](https://insights.sbomify.com/CVE-2023-24823/): RIOT-OS vulnerable to Packet Type Confusion during IPHC send (critical 9.8)
- [CVE-2021-27357](https://insights.sbomify.com/CVE-2021-27357/): Memory corruption in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-66647 and fix it if it is affected.

What it is: CVE-2025-66647 is a low-severity memory corruption vulnerability in RIOT-OS RIOT, published on 17 Dec 2025. 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-2025-66647 in the wild and no public exploit code.

Affected product: RIOT-OS RIOT. 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-2025-66647/ (Markdown: https://insights.sbomify.com/CVE-2025-66647/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-66647
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-66647
- OSV: https://osv.dev/vulnerability/CVE-2025-66647

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-66647/
Summaries are generated and may contain mistakes; the official description above is the record.