OPNsense core 26.1.6 through 26.7.7 contains an authentication bypass vulnerability in the captive portal roaming feature that lets unauthenticated attackers hijack authorized client sessions by spoofing unauthenticated MAC-to-IP observations. Attackers on the same Layer-2 segment can send forged gratuitous ARP replies binding their IP to a victim's MAC, gaining portal access with traffic attributed to the victim.