# CVE-2025-66647: RIOT is an open-source microcontroller operating system, designed to match the requirements of Internet of Things…

Source: https://junglewise.ai/threats/cve-2025-66647-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-2025-66647 · Severity: critical · CVSS 9.8 · 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 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.

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

## Quick answers

**Is CVE-2025-66647 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2025-66647 being exploited in the wild.

**How severe is CVE-2025-66647?** Critical severity, with a CVSS score of 9.8, 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-2025-66647?** 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-2025-66647?** 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)