The Advanced Google reCAPTCHA plugin for WordPress is vulnerable to IP unblocking in all versions up to, and including, 1.25. This is due to the plugin not utilizing a strong unique key when generating an unblock request. This makes it possible for unauthenticated attackers to unblock their IP after being locked out due to too many bad password attempts
The product uses a scheme that generates numbers or identifiers that are more predictable than required.