Reference page — cumulative record through Wednesday, August 19, 2026 UTC. Reference pages update as the archive grows; only dated daily editions are immutable pages of record.
zephyrproject zephyr — Broken IPv6 Neighbor Discovery input validation allows spoofed RA/NS/NA acceptance in Zephyr net stack
AV AC PR UI S C I A CVSS EPSS %ile KEV
A H N N U N H H 6.8 .0031 24.0 —
AFFECTED
Product Versions Fixed
zephyr 1.14.0 – —
TIMELINE
May 1 Reserved by zephyr
Jun 29 EXPLOIT PUBLISHED — CVE-2026-7656 (zephyrproject zephyr). Public exploit reference added.
Jun 29 Published (CNA: zephyr)
Aug 6 EXPLOIT PUBLISHED — CVE-2026-7656 (zephyrproject zephyr). Public exploit reference added.
Aug 6 RESCORED — CVE-2026-7656 (zephyrproject zephyr). CVSS 8.1 → 6.8 (NVD).
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 otherwise be rejected — can have forged Router Advertisement, Neighbor Solicitation, and Neighbor Advertisement messages accepted. A forged RA lets the attacker reconfigure the victim's default router, on-link prefixes (SLAAC), MTU, reachable/retransmit timers, and (with CONFIG_NET_IPV6_RA_RDNSS) DNS servers, while forged NS/NA enable neighbor-cache poisoning, enabling man-in-the-middle, traffic redirection, and denial of service. The flaw is an input-validation/authentication weakness rather than a memory-safety issue: the underlying packet-parsing primitives (net_pkt_get_data, net_pkt_read, net_pkt_skip) are independently bounds-safe and the validated length is the true buffer length, so skipping the length check causes no out-of-bounds access. The defect has existed since the logic was introduced in 2018 and shipped in all releases through v4.4.0; it is fixed by splitting the condition so any failing check drops the packet.
Lifecycle
Complete event history — 5 events, chronological
| Date | Event | Detail |
|---|
| May 1, 2026 | Reserved | Reserved by zephyr |
| June 29, 2026 | EXPLOIT PUBLISHED | EXPLOIT PUBLISHED — CVE-2026-7656 (zephyrproject zephyr). Public exploit reference added. |
| June 29, 2026 | Published | Published (CNA: zephyr) |
| August 6, 2026 | EXPLOIT PUBLISHED | EXPLOIT PUBLISHED — CVE-2026-7656 (zephyrproject zephyr). Public exploit reference added. |
| August 6, 2026 | RESCORED | RESCORED — CVE-2026-7656 (zephyrproject zephyr). CVSS 8.1 → 6.8 (NVD). |
Affected
Affected products and packages — 1 row
| Vendor | Product / Package | Ecosystem | Version introduced | Fixed |
|---|
| zephyrproject | zephyr | — | 1.14.0 | — |
About this page
This is a reference page, not a dated page of record. It assembles the complete lifecycle of CVE-2026-7656 from the CVE Program record, NVD enrichment, the CISA KEV catalog, EPSS, and OSV advisories. The box score's numbers (CVSS, EPSS, KEV status) are current as of Wednesday, August 19, 2026 UTC and are re-derived as the archive grows; only dated daily editions are immutable pages of record. The authoritative source for this identifier is cve.org.