ExampleNullByteVulnerability.php

<?php
function nice_include($file) {
  if (file_exists('/home/wwwrun/'.$file.'.php')) { // Taken from PHP docs
   include '/home/wwwrun/'.$file.'.php';
  }
}

nice_include("../private_admin_data.txt\0");
# => file_exists will return true since home/private_admin_data.txt exists
# => The '.php' extension will be skipped because of the \0 null-termination character.
?>