CVE-2026-12633

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Memory Corruption in Zephyr RTOS IPv6 Neighbor Discovery

Publication date: 2026-08-19

Last updated on: 2026-08-26

Assigner: Zephyr Project

Description

The IPv6 neighbor-discovery code in subsys/net/ip/ipv6_nbr.c processes the 6LoWPAN Context Option (6CO, RFC 6775) carried inside ICMPv6 Router Advertisements. In handle_ra_6co() the 8-bit context_len field is taken directly from the packet and was never bounded to the RFC maximum of 128. The function computes context->context_len / 8 and then performs memset(context->prefix + context_len, 0, sizeof(context->prefix) - context_len), where context->prefix is a fixed 16-byte array. With context_len between 136 and 255 (and the option length field set to 3, which the pre-fix validation accepts), context_len / 8 evaluates to 17..31, so the memset length 16 - context_len/8 underflows the unsigned size_t argument to roughly SIZE_MAX. This produces an unbounded out-of-bounds memset that zeroes kernel memory well past the 6lo context structure. The defect is reachable from unauthenticated, link-local input: any host on the same link can send a crafted Router Advertisement with a 6CO option. The RA handler validates only the option length field before calling handle_ra_6co(), so a single packet triggers the wild write. The code is compiled when CONFIG_NET_6LO_CONTEXT is enabled. The impact is a reliable remote (adjacent) denial of service via memory corruption, with collateral integrity loss as the memset zeroes contiguous memory before the system faults. Router Advertisements are link-scoped and not forwarded, so the attacker must be on the same link (AV:A). The fix rejects any context_len greater than 128 before the length computation.

CVSS Scores

EPSS Scores

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Meta Information

Published

2026-08-19

Last Modified

2026-08-26

Generated

2026-09-09

AI Q&A

2026-08-20

EPSS Evaluated

2026-09-07

NVD

CVE-2026-12633

Affected Vendors & Products

Vendor	Product	Version / Range
zephyrproject	zephyr	to 128 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-787	The product writes data past the end, or before the beginning, of the intended buffer.

Attack-Flow Graph

Executive Summary

This vulnerability is in the IPv6 neighbor-discovery code of the Zephyr RTOS. It involves improper handling of the 6LoWPAN Context Option (6CO) in ICMPv6 Router Advertisements. The code fails to validate the 8-bit context_len field, allowing values up to 255 instead of the RFC-mandated maximum of 128. This leads to an unbounded out-of-bounds memset operation that corrupts kernel memory, causing a denial of service and potential integrity loss.

Detection Guidance

This vulnerability is triggered by crafted IPv6 Router Advertisements with a 6LoWPAN Context Option (6CO) containing a context_len field between 136 and 255. Detection requires monitoring for malformed RA packets on the local network. Use tools like tcpdump to capture ICMPv6 Router Advertisements and inspect the 6CO option for invalid context_len values. Example command: tcpdump -i <interface> -vv 'icmp6 and ip6[40] == 134' | grep '6CO'.

Impact Analysis

The vulnerability allows an unauthenticated attacker on the same network link to crash the system via a crafted Router Advertisement packet. This results in a remote denial of service and possible memory corruption. The attack requires physical or logical access to the local network segment.

Compliance Impact

This vulnerability does not directly affect compliance with GDPR or HIPAA as it involves a denial-of-service and memory corruption issue in network protocol handling. However, if exploited, it could lead to system instability or crashes, potentially disrupting services that handle sensitive data, indirectly impacting compliance.

Mitigation Strategies

Apply the vendor patch that rejects context_len values greater than 128. If a patch is unavailable, disable CONFIG_NET_6LO_CONTEXT in the kernel configuration to prevent the vulnerable code from being compiled. Additionally, restrict access to the local network segment to trusted hosts to reduce attack surface.

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