An issue was discovered on Actiontec WCB6200Q before 184.108.40.206a devices. The admin login session cookie is insecurely generated making admin session hijacking possible. When an admin logs in, a session cookie is generated using the time of day rounded to 10ms. Since the web server returns its current time of day in responses, it is possible to step backward through possible session values until a working one is found. Once a working session ID is found, an attacker then has admin control of the device and can add a secondary SSID to create a backdoor to the network.
CWE-384 - Session Fixation
Authenticating a user, or otherwise establishing a new user session, without invalidating any existing session identifier gives an attacker the opportunity to steal authenticated sessions.