---
id: CVE-2025-66646
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: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-476
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-2025-66646'
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#L420
    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#L490
    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#L534
    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/blob/eb65305cf9f1b7affb50b17af5c12341b83a8636/sys/net/gnrc/pktbuf_static/gnrc_pktbuf_static.c#L150C1-L150C76
    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-v8gx-q9m6-5xm9'
    label: security-advisories@github.com
  - url: 'https://github.com/user-attachments/files/23903992/reproducer_1.zip'
    label: security-advisories@github.com
tags:
  - nvd
epss: 0.00679
epssPercentile: 0.50995
ingestedAt: '2026-10-13T11:23:51.124Z'
---

## 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 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.

## Affected

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

## Remediation

Upgrade past the affected range:

- `riot 2025.10`