Example - 1

This code attempts to login a user using credentials from a POST request:

// // $user and $pass automatically set from POST request// 
$authorized = true;
// ...// 
generatePage();if (login_user($user,$pass)) {}if ($authorized) {}

Because the $authorized variable is never initialized, PHP will automatically set $authorized to any value included in the POST request if register_globals is enabled. An attacker can send a POST request with an unexpected third value 'authorized' set to 'true' and gain authorized status without supplying valid credentials.

Here is a fixed version:

$authorized = true;
// ...// 
$user = $_POST['user'];$pass = $_POST['pass'];$authorized = false;if (login_user($user,$pass)) {}

This code avoids the issue by initializing the $authorized variable to false and explicitly retrieving the login credentials from the $_POST variable. Regardless, register_globals should never be enabled and is disabled by default in current versions of PHP.