CVE-2025-66647

CRITICAL
Published Dec 17, 2025 Modified Jan 22, 2026 CWE-120

Description

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.

CVSS v3.1 Score

9.8
CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Weakness Type (CWE)

CWE-120 CWE-120

Affected Products

Vendor Product
riot-os riot
riot-os riot
riot-os riot
riot-os riot

References

Frequently Asked Questions

What is CVE-2025-66647? +
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. It has a CVSS v3.1 base score of 9.8 (CRITICAL).
How severe is CVE-2025-66647? +
CVE-2025-66647 has a CVSS v3.1 score of 9.8 out of 10, rated CRITICAL. This is a critical vulnerability that should be patched immediately.
What products are affected by CVE-2025-66647? +
CVE-2025-66647 affects products from riot-os, specifically: riot. Check the affected products table above for specific version ranges.
How do I check if I'm vulnerable to CVE-2025-66647? +
You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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