CVE-2026-7656: input-validation in zephyrproject zephyr
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.
AI Analysis
Technical Summary
The IPv6 Neighbor Discovery (ND) handlers in Zephyr's subsys/net/ip/ipv6_nbr.c contain a logic error in the boolean expression that validates ND messages. The condition combined RFC 4861 validity checks with an ICMPv6 code check using incorrect operator precedence, causing the entire predicate to evaluate false when the ICMPv6 code is 0 (the normal value). This results in skipping mandatory checks such as Hop Limit == 255, source address validation for Router Advertisements, and multicast-target sanity checks. Consequently, an adjacent on-link attacker, and potentially a remote attacker due to the bypassed Hop Limit check, can send forged ND messages that are accepted by the victim. These forged messages can manipulate the victim's network configuration (default router, prefixes, MTU, timers, DNS servers) and enable neighbor-cache poisoning, leading to man-in-the-middle, traffic redirection, and denial of service attacks. The vulnerability is an input-validation/authentication weakness, not a memory safety issue. It has existed since 2018 and affects all releases through version 4.4.0. The fix involves splitting the condition so that any failing check causes the packet to be dropped.
Potential Impact
An attacker can bypass critical IPv6 Neighbor Discovery validation checks, allowing forged Router Advertisement, Neighbor Solicitation, and Neighbor Advertisement messages to be accepted. This enables network configuration manipulation, neighbor-cache poisoning, man-in-the-middle attacks, traffic redirection, and denial of service. Both adjacent on-link attackers and potentially remote/off-link attackers can exploit this due to the bypassed Hop Limit check. The vulnerability does not cause memory corruption but compromises network protocol authentication and integrity.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. The vulnerability is fixed by correcting the boolean logic in the IPv6 ND handlers to ensure all validity checks are enforced and packets failing any check are dropped. Until a patch is applied, network administrators should be aware of the risk of forged ND messages and consider network-level protections against rogue IPv6 ND traffic where feasible.
CVE-2026-7656: input-validation in zephyrproject zephyr
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.
CVSS v3.1
Score 8.1high
Affected software
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AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The IPv6 Neighbor Discovery (ND) handlers in Zephyr's subsys/net/ip/ipv6_nbr.c contain a logic error in the boolean expression that validates ND messages. The condition combined RFC 4861 validity checks with an ICMPv6 code check using incorrect operator precedence, causing the entire predicate to evaluate false when the ICMPv6 code is 0 (the normal value). This results in skipping mandatory checks such as Hop Limit == 255, source address validation for Router Advertisements, and multicast-target sanity checks. Consequently, an adjacent on-link attacker, and potentially a remote attacker due to the bypassed Hop Limit check, can send forged ND messages that are accepted by the victim. These forged messages can manipulate the victim's network configuration (default router, prefixes, MTU, timers, DNS servers) and enable neighbor-cache poisoning, leading to man-in-the-middle, traffic redirection, and denial of service attacks. The vulnerability is an input-validation/authentication weakness, not a memory safety issue. It has existed since 2018 and affects all releases through version 4.4.0. The fix involves splitting the condition so that any failing check causes the packet to be dropped.
Potential Impact
An attacker can bypass critical IPv6 Neighbor Discovery validation checks, allowing forged Router Advertisement, Neighbor Solicitation, and Neighbor Advertisement messages to be accepted. This enables network configuration manipulation, neighbor-cache poisoning, man-in-the-middle attacks, traffic redirection, and denial of service. Both adjacent on-link attackers and potentially remote/off-link attackers can exploit this due to the bypassed Hop Limit check. The vulnerability does not cause memory corruption but compromises network protocol authentication and integrity.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. The vulnerability is fixed by correcting the boolean logic in the IPv6 ND handlers to ensure all validity checks are enforced and packets failing any check are dropped. Until a patch is applied, network administrators should be aware of the risk of forged ND messages and consider network-level protections against rogue IPv6 ND traffic where feasible.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- zephyr
- Date Reserved
- 2026-05-01T18:40:20.792Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a42f37c27e9c797199f758c
Added to database: 06/29/2026, 22:36:44 UTC
Last enriched: 08/07/2026, 13:33:45 UTC
Last updated: 08/08/2026, 13:34:30 UTC
Views: 161
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