---
id: CVE-2026-19577
title: >-
  net_route_ipv6_packet() in subsys/net/ip/route_ipv6.c resolved the nexthop's
  link-layer address with net_nbr_get_lladdr(nbr->idx) without first checking
  whether the neighbor cache entry actually had a linked link-layer address
summary: >-
  net_route_ipv6_packet() in subsys/net/ip/route_ipv6.c resolved the nexthop's
  link-layer address with net_nbr_get_lladdr(nbr->idx) without first checking
  whether the neighbor cache entry actually had a linked link-layer address. An
  unreso…
severity: high
cvss: 7.1
cvssVector: 'CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H'
cwe:
  - CWE-125
published: '2026-10-11'
updated: '2026-10-11'
sourceUpdated: '2026-10-11T18:16:58.433'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-19577'
references:
  - url: >-
      https://github.com/zephyrproject-rtos/zephyr/commit/b0b0e8973d1967114adbb9ed1611d448b5a46519
    label: vulnerabilities@zephyrproject.org
  - url: >-
      https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-vv76-4m89-95q5
    label: vulnerabilities@zephyrproject.org
tags:
  - nvd
ingestedAt: '2026-10-12T14:50:34.065Z'
---

## Overview

net_route_ipv6_packet() in subsys/net/ip/route_ipv6.c resolved the nexthop's link-layer address with net_nbr_get_lladdr(nbr->idx) without first checking whether the neighbor cache entry actually had a linked link-layer address. An unresolved neighbor carries idx == NET_NBR_LLADDR_UNKNOWN (0xff), and net_nbr_get_lladdr() in subsys/net/ip/nbr.c performs no runtime bounds check beyond a NET_ASSERT, returning &net_neighbor_lladdr[255] — roughly 2.5 KB past the end of an array whose default size is CONFIG_NET_IPV6_MAX_NEIGHBORS (8). Because the returned pointer is never NULL, the following lladdr == NULL guard does not catch it.

The function is reached from ipv6_route_packet() in subsys/net/ip/ipv6.c for every received unicast IPv6 packet whose destination is not a local address on the receiving interface; CONFIG_NET_IPV6_ROUTE is enabled by default whenever the IPv6 neighbor cache is, so no router or forwarding configuration is needed. net_route_ipv6_get_info() returns the packet's destination itself as the nexthop when a neighbor cache entry for it exists, and the cache lookup does not skip INCOMPLETE entries. An unauthenticated attacker on the same link can therefore force the unresolved state — for example by eliciting traffic to a spoofed, non-existent neighbor address so that net_ipv6_send_ns() creates an INCOMPLETE entry, or by sending a Router Advertisement with no source link-layer address option, which creates a persistently unresolved router neighbor — and then send a packet addressed to that neighbor.

The result is an out-of-bounds read at a fixed index past the neighbor link-layer address array. On builds with CONFIG_ASSERT enabled the assertion fires and the device panics, giving a repeatable remote denial of service. With assertions disabled, the stale out-of-bounds struct net_linkaddr drives a memcmp() over an attacker-uninfluenced length and, when its len byte passes the NET_LINK_ADDR_MAX_LENGTH check, up to 8 bytes of unrelated static RAM are copied into the outgoing frame's destination link-layer address and transmitted on the link, disclosing them to any listener. There is no out-of-bounds write and the offset is not attacker-controlled, which bounds the impact.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.