---
id: CVE-2025-66647
title: >-
  RIOT is an open-source microcontroller operating system, designed to match the
  requirements of Internet of Things (IoT) devices and other embedded devices
summary: >-
  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
  implementatio…
severity: critical
cvss: 9.8
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'
cwe:
  - CWE-120
vendor: riot-os
product: riot
affected:
  - riot < 2025.10
  - riot = 2025.10
patched:
  - riot 2025.10
published: '2025-12-17'
updated: '2026-10-13'
sourceUpdated: '2026-10-13T11:10:00.203'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2025-66647'
references:
  - url: >-
      https://github.com/RIOT-OS/RIOT/blob/eb65305cf9f1b7affb50b17af5c12341b83a8636/sys/net/gnrc/network_layer/ipv6/ext/frag/gnrc_ipv6_ext_frag.c#L411
    label: security-advisories@github.com
  - url: >-
      https://github.com/RIOT-OS/RIOT/blob/eb65305cf9f1b7affb50b17af5c12341b83a8636/sys/net/gnrc/network_layer/ipv6/ext/frag/gnrc_ipv6_ext_frag.c#L481
    label: security-advisories@github.com
  - url: >-
      https://github.com/RIOT-OS/RIOT/blob/eb65305cf9f1b7affb50b17af5c12341b83a8636/sys/net/gnrc/network_layer/ipv6/ext/frag/gnrc_ipv6_ext_frag.c#L532
    label: security-advisories@github.com
  - url: >-
      https://github.com/RIOT-OS/RIOT/blob/eb65305cf9f1b7affb50b17af5c12341b83a8636/sys/net/gnrc/network_layer/ipv6/ext/frag/gnrc_ipv6_ext_frag.c#L544
    label: security-advisories@github.com
  - url: 'https://github.com/RIOT-OS/RIOT/releases/tag/2025.10'
    label: security-advisories@github.com
  - url: 'https://github.com/RIOT-OS/RIOT/security/advisories/GHSA-wh3v-q6vr-j79r'
    label: security-advisories@github.com
tags:
  - nvd
epss: 0.00971
epssPercentile: 0.60919
ingestedAt: '2026-10-13T11:23:51.125Z'
---

## Overview

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.

## Affected

- `riot < 2025.10`
- `riot = 2025.10`

## Remediation

Upgrade past the affected range:

- `riot 2025.10`