# CVE-2025-66646: RIOT-OS has NULL pointer dereference in gnrc_ipv6_ext_frag_reass

> Attacker can crash RIOT OS by sending crafted IPv6 packets if the fragmentation module is enabled, requiring an upgrade to fix.

- **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-v8gx-q9m6-5xm9

## What is CVE-2025-66646?

CVE-2025-66646 is a low-severity 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 receiving an fragmented IPv6 packet with fragment offset 0 and an empty payload, the payload pointer is set to NULL. However, the implementation still tries to copy the payload into the reassembly buffer, resulting in a NULL pointer dereference which crashes the OS (DoS). To trigger the vulnerability, the `gnrc_ipv6_ext_frag` module must be enabled and the attacker must be able to send arbitrary IPv6 packets to the victim. RIOT OS v2025.10 fixes the issue.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2025-66646?

It affects 1 product.


Products: Riot-Os Riot.

## How do I fix CVE-2025-66646?

No fix has been published for CVE-2025-66646 yet. Limit exposure of the affected software until one is available.

## Is CVE-2025-66646 being exploited?

There is no known exploitation of CVE-2025-66646 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-2025-66646 and fix it if it is affected.

What it is: CVE-2025-66646 is a low-severity 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-2025-66646 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-2025-66646/ (Markdown: https://insights.sbomify.com/CVE-2025-66646/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-66646
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-66646
- OSV: https://osv.dev/vulnerability/CVE-2025-66646

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-66646/
Summaries are generated and may contain mistakes; the official description above is the record.