OverTheWire - Natas - Level 1 → Level 2

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1.) you want to see a possible alternative solution or
2.) you are stuck and need a hint!

Login using given credentials.

Username: natas2
Password: Zlurxxxxxxxxxxxxxxxxxxxxxxxxxxxx
URL:      http://natas2.natas.labs.overthewire.org

The message on the page is:

There is nothing on this page

A look into the source code of the page shows that a 1x1 pixel image is included.

<div id="content">
There is nothing on this page
<img src="files/pixel.png">

This seems to be an uninteresting PNG image. Checking it using file and strings don't reveal something interesting.
Next check is to take a look to the contents of the files/ folder, which shows up a file called users.txt because directory listing is enabled in the Apache configuration.
The password for the next level is found in this file.

# username:password
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