CVE-2025-66647
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedRIOT 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.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceRIOT OS v2025.07 has a buffer overflow vulnerability in the IPv6 fragmentation reassembly code (gnrc_ipv6_ext_frag module). When copying the first fragment (offset=0) into the reassembly buffer, no size validation occurs. Attackers can exploit this by first sending a short fragment to create a small buffer, then sending a larger fragment that overflows the buffer, corrupting adjacent packet buffer state and potentially achieving remote code execution.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data< 2025.10= 2025.10CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Determine the RIOT OS firmware versionCheck the VERSION file in the RIOT repository or the firmware build metadata. On a running device, this may be visible in boot logs, via a version command if available, or by inspecting the firmware binary strings for version identifiers like '2025.07', '2025.08', '2025.09', or '2025.10'.Affected if The installed version is 2025.07, 2025.08, 2025.09, or 2025.10 (versions below 2025.10 are affected)
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Verify if the gnrc_ipv6_ext_frag module is included in the buildExamine the application's Makefile for 'USEMODULE += gnrc_ipv6_ext_frag' or check the compiled binary's symbol table for functions from this module (e.g., gnrc_ipv6_ext_frag_buf). If using a build system, check the build configuration for this module.Affected if The gnrc_ipv6_ext_frag module is compiled into the firmware and the device uses IPv6 fragmentation reassembly
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Confirm IPv6 is enabled and fragmentation is in useCheck the application's Makefile or Kconfig for 'USEMODULE += gnrc_ipv6' and verify that IPv6 is actually being used in the deployment. Also check if any IPv6-based protocols (like 6LoWPAN) that might trigger fragmentation are enabled.Affected if IPv6 is enabled and the device is expected to receive fragmented IPv6 packets from the network
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Check network exposure to untrusted IPv6 sourcesReview network configuration and firewall rules to determine whether the device can receive IPv6 packets from untrusted or external network sources. Fragmented IPv6 packets would need to reach the device.Affected if The device processes IPv6 packets from untrusted or uncontrolled network sources
A user is affected if they are running RIOT OS versions 2025.07 through 2025.10, the gnrc_ipv6_ext_frag module is compiled in, IPv6 is enabled, and the device can receive fragmented IPv6 packets from the network.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped2025.10
Upgrade to RIOT OS v2025.10 or later. If upgrade is not immediately feasible, consider disabling the gnrc_ipv6_ext_frag module if IPv6 fragmentation is not required, and restrict network access to trusted sources.
2025.10 or later
- 1. Identify all RIOT OS deployments using version 2025.07 or earlier that have the `gnrc_ipv6_ext_frag` module enabled
- 2. Identify all deployments currently running version 2025.10 (which still contains the vulnerability)
- 3. Upgrade all affected deployments to RIOT OS version 2025.10 or later (the official description states version 2025.10 fixes the issue)
- 4. Verify the upgrade by checking the RIOT version string on each device
- 5. Ensure network filters are in place to limit IPv6 packet sources until the upgrade is complete, as the vulnerability can be triggered by arbitrary IPv6 packets
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation3.0 h
- Implementation4.0 h
- Testing4.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2025-66647 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2025-66647 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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