The white box says "There is nothing on this page".
Here is the page’s code (without the header):
<body> <h1>natas2</h1> <div id="content"> There is nothing on this page <img src="files/pixel.png"> </div> </body></html>
Hmmm, what is this files/pixel.png? If we look at it, it is just a white pixel image.
However, we now know that there is a folder named files. We navigate to http://natas2.natas.labs.overthewire.org/files/. We see an Index of /files that contains links to the parent directory, pixel.png, and a file named users.txt.
Here is the contents of users.txt:
# username:password alice:BYNdCesZqW bob:jw2ueICLvT charlie:G5vCxkVV3m natas3:sJIJNW6ucpu6HPZ1ZAchaDtwd7oGrD14 eve:zo4mJWyNj2 mallory:9urtcpzBmH