# CVE-2025-66646: RIOT is an open-source microcontroller operating system, designed to match the requirements of Internet of Things…

Source: https://junglewise.ai/threats/cve-2025-66646-riot-is-an-open-source-microcontroller-operating-system-designed  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2025-12-17  
License: CC BY 4.0 with a link back

CVE-2025-66646 · Severity: high · CVSS 7.5 · Published 2025-12-17

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.

Technologies: [Riot-Os Riot](https://junglewise.ai/threats/technologies/riot). Vendors: [Riot-Os](https://junglewise.ai/threats/vendors/riot-os).

## Quick answers

**Is CVE-2025-66646 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2025-66646 being exploited in the wild.

**How severe is CVE-2025-66646?** High severity, with a CVSS score of 7.5, published 17 December 2025.

**Which products and versions are affected?** Riot-Os Riot. The advisory does not name versions.

**Is there a fix for CVE-2025-66646?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**Am I affected by CVE-2025-66646?** Check whether you run Riot-Os Riot. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Affected products

- Riot-Os Riot

## Related threats

- [RIOT DHCPv6 client out-of-bounds heap read](https://junglewise.ai/threats/cve-2026-49868-riot-is-an-open-source-microcontroller-operating-system-designed)
- [RIOT nanocoap integer overflow in Block2 option parsing](https://junglewise.ai/threats/cve-2026-102692-riot-is-an-open-source-microcontroller-operating-system-designed)
- [RIOT nanocoap_fileserver assertion failure in response handling](https://junglewise.ai/threats/cve-2026-107838-riot-is-an-open-source-microcontroller-operating-system-designed)
- [RIOT operating system out-of-bounds read in 6LoWPAN fragment handling](https://junglewise.ai/threats/cve-2026-107837-riot-is-an-open-source-microcontroller-operating-system-designed)
- [RIOT nanoCoAP client buffer underflow in blockwise transfer](https://junglewise.ai/threats/cve-2026-107836-riot-is-an-open-source-microcontroller-operating-system-designed)