CVE-2026-7656

Technical Description

The IPv6 Neighbor Discovery handlers in subsys/net/ip/ipv6_nbr.c (handle_ra_input, handle_ns_input, handle_na_input) used an incorrect boolean expression that combined the RFC 4861 validity checks with the ICMPv6 code check using the wrong operator precedence: the form was ((length/hop/source/target checks) && (icmp_hdr->code != 0)). Because every legitimate ND message carries ICMPv6 code 0, an attacker setting code == 0 (the normal value) caused the entire predicate to evaluate false, so the packet was never dropped and all of the other checks were silently skipped. The bypassed checks include the mandatory Hop Limit == 255 verification (which proves an ND packet originated on-link and was not forwarded) and, for Router Advertisements, the requirement that the source be a link-local address, as well as multicast-target sanity checks. As a result, an adjacent on-link attacker — and, because the Hop-Limit-255 guard is bypassed, potentially a remote/off-link attacker whose packets would

Remediation

Check the references section for vendor advisories and patches from zephyrproject. Update zephyr to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

Affected Products

References