zephyrproject zephyr up to 4.4.x subsys/net/ip/ipv6_nbr.c regular control flow

Summaryinfo

A vulnerability classified as problematic has been found in zephyrproject zephyr up to 4.4.x. Affected by this vulnerability is an unknown functionality of the file subsys/net/ip/ipv6_nbr.c. This manipulation of the argument regular causes control flow. This vulnerability is tracked as CVE-2026-7656. The attack is only possible within the local network. No exploit exists. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability has been found in zephyrproject zephyr up to 4.4.x and classified as problematic. Affected by this vulnerability is some unknown processing of the file subsys/net/ip/ipv6_nbr.c. The manipulation of the argument normal with an unknown input leads to a control flow vulnerability. The CWE definition for the vulnerability is CWE-670. The code contains a control flow path that does not reflect the algorithm that the path is intended to implement, leading to incorrect behavior any time this path is navigated. As an impact it is known to affect integrity, and availability. The summary by CVE is:

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.

The advisory is shared at github.com. This vulnerability is known as CVE-2026-7656 since 05/01/2026. The exploitation appears to be easy. Access to the local network is required for this attack to succeed. Technical details are known, but no exploit is available.

Upgrading to version 4.5.0 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-40237). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Type

• Project Management Software

Vendor

• zephyrproject

Name

• zephyr

Version

• 4.0
• 4.1
• 4.2
• 4.3
• 4.4

CPE 2.3info

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CPE 2.2info

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Entryinfo

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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