Login No Captcha reCAPTCHA < 1.8.1 - Unauthenticated Stored Cross-Site Scripting via PHP_SELF

Description

The Login No Captcha reCAPTCHA plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the `$_SERVER['PHP_SELF']` superglobal in all versions up to, and including, 1.8.0. This is due to the `authenticate()` function storing the unsanitized output of `basename($_SERVER['PHP_SELF'])` in the `login_nocaptcha_error` WordPress option when a login attempt is made from a non-standard login page (e.g., xmlrpc.php). The `admin_notices()` function then echoes this stored value directly into the admin dashboard HTML without escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts that execute when an administrator with a whitelisted IP address visits the WordPress dashboard within 30 seconds of the attack.