In this podcast I discuss a type of attack that allows users to basicly do things they are not supposed to do, without ever having to hack the admin type of accounts. So without having to figure out the admin password it is often possible to do administrative functions by simply attempting them.
The problem is around validation against access controls at every point of execution. Too often the access controls are done to control the navigational structure, meaning that the menus do not have links to the admin functionality, but if you know what the URL is then you can just type it into your browser and get there. Thats bad design in the app, and it is VERY common.