CVE-2026-19577 Out-of-bounds read in IPv6 route forwarding when the nexthop neighbor has no link-layer address

netrouteipv6packet in subsys/net/ip/routeipv6.c resolved the nexthop's link-layer address with netnbrgetlladdrnbr-idx without first checking whether the neighbor cache entry actually had a linked link-layer address. An unresolved neighbor carries idx == NETNBRLLADDRUNKNOWN 0xff, and netnbrgetllad...