CVE-2025-66646: Riot-OS Riot

High severity, CVSS 7.5. EPSS: 0.7% chance of exploitation in the next 30 days.

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 products

• Riot-OS Riot: before 2025.10 (fixed in 2025.10); version 2025.10 only

Published 2025-12-17. Last modified 2026-06-17.