The Zyxel P-2602HW-D1A router with 3.40(AJZ.1) firmware maintains authentication state by IP address, which allows remote attackers to bypass authentication by establishing a session from a source IP address of a user who previously authenticated within the previous 5 minutes.
https://exchange.xforce.ibmcloud.com/vulnerabilities/41112
http://www.securityfocus.com/archive/1/489009/100/0/threaded