Based on one of the lectures of Planning, Auditing and Maintaining Enterprise system course by Greg Williams (Department of computer science university of Colorado):
Let's say they were installing a service on a Linux system and we forget to take down the installation page. That installation page has a lot of sensitive information on it. so, if we leave that page up and don't delete it out of the directory after installation, that's a way for an attacker to get in.
How It becomes possible?