CVE-2026-13735 WireGuard keepalive transport-data messages accepted without Poly1305 authentication

Zephyr's WireGuard implementation in subsys/net/lib/wireguard/wgcrypto.c mishandled keepalive packets. In wgprocessdatamessage, any type-4 transport-data message whose payload was exactly 16 bytes an empty plaintext plus a bare Poly1305 tag, i.e. a keepalive was accepted and returned immediately,...