I was giving this some real thought as well. I think the webserver (apache) runs as a separate process from the server dashboard/console. That is, if a user has access to the webserver, all they can do is what you can do through either the default.htm or UI2.htm web pages. I may be totally off base, but I just don't see the someone can elevate their privileges, or create other users from the webserver. If they had access to the BI console (by way of RDP or something like VNC/Teamviewer) absolutely. Likewise, I don't think they can see each camera's properties such as username/password - or even IP address (unless you're using the IP address as the name of the camera).
In my case, I have all of my cameras on a separate subnet which is blocked from any (in or out) internet access - so they cannot be accessed from the WAN.
Still, in an over-abundance of caution, I've changed all my user passwords, enabled SSL (secure) on the server, and disabled the ROKU app.
I've also sent an email to Ken asking him if there is any auto-ban and IP whitelisting routine that he could add to the webserver. My filezilla FTP server has a fantastic IP validation process. I can block ALL incoming IP addresses, except those I've specifically allowed. And whitelisting a range is just as easy. For example, I can allow 24.*.*.* and 172.*.*.* - which are blocks assigned to specific geo-locations and ISPs. It makes attacks by users outside the US much more difficult. I currently have about 20 octets in my whitelist, and have not had any problems getting to my FTP from anywhere I might be logging in.
The auto-ban is great for eliminating brute-force attacks. If the same IP has a failed log attempt more than X times, block that IP for X hours (or indefinitely).
I'm hoping that Ken can incorporate such firewall measures on the webserver.