CWE-290

uRPF performs reverse routing lookup on every incoming packet’s source address — if the packet arrived on the wrong interface, it’s spoofed and dropped. When uRPF is disabled (the enterprise wireless default due to asymmetric routing), any host on the L2 segment can claim any source IP unconditionally. This is CWE-290 at Layer 3. Three confirmed attack classes in ArubaOS AOS-8: Smurf amplification (spoofed src → broadcast → victim flood), ICMP Timestamp leak (impersonate trusted management IP → elicit timestamp response), pre-auth reflection (use controller as intermediary). Single-packet pcap signature included. Linux sysctl and Cisco IOS uRPF configuration provided.

Smurf amplification requires three weaknesses simultaneously: no uRPF allows IP source spoofing, directed broadcast forwarding delivers the packet to all VLAN hosts, hosts reply to broadcast ICMP Echo. RFC 2644 fixed router-level directed broadcast. L2 broadcast domains are unaffected — the packet never crosses a router. Enterprise wireless VLANs with 50-100 APs and controllers become 50-100x amplifiers. ICMP processing is pre-authentication: no credentials, no session. Two-machine verification: attacker sends spoofed src=victim to broadcast, victim captures unsolicited Echo Replies. pcap-level proof included.