CVE-2025-66646

HIGH
Published Dec 17, 2025 Modified Jan 22, 2026 CWE-476

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 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.

Is your site exposed to CVE-2025-66646?

Run a free security scan — no signup, results in seconds.

CVSS v3.1 Score

7.5
HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Weakness Type (CWE)

CWE-476 CWE-476

Affected Products

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

References

Other References

https://github.com/RIOT-OS/RIOT/blob/eb65305cf9f1b7affb50b17af5c12341b83a8636/sys/net/gnrc/network_layer/ipv6/ext/frag/gnrc_ipv6_ext_frag.c#L411 https://github.com/RIOT-OS/RIOT/blob/eb65305cf9f1b7affb50b17af5c12341b83a8636/sys/net/gnrc/network_layer/ipv6/ext/frag/gnrc_ipv6_ext_frag.c#L420 https://github.com/RIOT-OS/RIOT/blob/eb65305cf9f1b7affb50b17af5c12341b83a8636/sys/net/gnrc/network_layer/ipv6/ext/frag/gnrc_ipv6_ext_frag.c#L490 https://github.com/RIOT-OS/RIOT/blob/eb65305cf9f1b7affb50b17af5c12341b83a8636/sys/net/gnrc/network_layer/ipv6/ext/frag/gnrc_ipv6_ext_frag.c#L532 https://github.com/RIOT-OS/RIOT/blob/eb65305cf9f1b7affb50b17af5c12341b83a8636/sys/net/gnrc/network_layer/ipv6/ext/frag/gnrc_ipv6_ext_frag.c#L534 https://github.com/RIOT-OS/RIOT/blob/eb65305cf9f1b7affb50b17af5c12341b83a8636/sys/net/gnrc/network_layer/ipv6/ext/frag/gnrc_ipv6_ext_frag.c#L544 https://github.com/RIOT-OS/RIOT/blob/eb65305cf9f1b7affb50b17af5c12341b83a8636/sys/net/gnrc/pktbuf_static/gnrc_pktbuf_static.c#L150C1-L150C76 https://github.com/RIOT-OS/RIOT/releases/tag/2025.10

Frequently Asked Questions

What is CVE-2025-66646? +
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. It has a CVSS v3.1 base score of 7.5 (HIGH).
How severe is CVE-2025-66646? +
CVE-2025-66646 has a CVSS v3.1 score of 7.5 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching.
What products are affected by CVE-2025-66646? +
CVE-2025-66646 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-2025-66646? +
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.

Related Vulnerabilities

CVE-2025-29896

A NULL pointer dereference vulnerability has been reported to affect Qsync Central. If a remote attacker gains a user account, …
CVE-2026-8479

IEC 60870-5-104 used in bidirectional mode in RTU500 is vulnerable for a NULL pointer dereferencing, if a specially crafted sequence …
CVE-2026-43841

A NULL pointer dereference vulnerability in the license manager service could allow an unauthenticated attacker to crash the service via …
CVE-2025-24031

PAM-PKCS#11 is a Linux-PAM login module that allows a X.509 certificate based user login. In versions 0.6.12 and prior, the …
CVE-2025-31115

XZ Utils provide a general-purpose data-compression library plus command-line tools. In XZ Utils 5.3.3alpha to 5.8.0, the multithreaded .xz decoder …
CVE-2025-0121

A null pointer dereference vulnerability in the Palo Alto Networks Cortex® XDR agent on Windows devices allows a low-privileged local …

Don't wait for an exploit

Scan your website for vulnerabilities like CVE-2025-66646 — free, no signup required.

Patch and protect

Block known exploits with a web application firewall while you patch, keep your own devices clean, or test the fix on a fresh server.

Compare VPS prices →
Sucuri Sucuri → Website firewall, malware cleanup & monitoring NordPass NordPass → Password manager with breach alerts Malwarebytes Malwarebytes → Anti-malware for Windows, Mac and phones, 25% off Contabo Contabo → Cheap VPS & dedicated servers, EU/US/Asia
ESET ESET → Antivirus & internet security, current coupons DigitalOcean DigitalOcean → Developer cloud: Droplets, managed databases, S3 storage NordVPN NordVPN → Hide your IP, servers in 120+ countries

Affiliate links: we may earn a commission, your price stays the same.