Some of the software on these routers is atrocious. I don't just mean the awful grammar and spelling in the ASUS router I bought, but I wouldn't be surprised at all if password checking was just something like:
var password = document.getElementById('password').value,
correctPass = 'foobar';
if (password == correctPass) window.location.href = "/secure/index.html";
Oh wait, this actually happens in practice!