The LOGIN AND REGISTRATION ATTEMPTS LIMIT plugin for WordPress is vulnerable to IP Address Spoofing in versions up to, and including, 2.1. This is due to insufficient restrictions on where the IP Address information is being retrieved for request logging and login restrictions. Attackers can supply the X-Forwarded-For header with with a different IP Address that will be logged and can be used to bypass settings that may have blocked out an IP address from logging in.
The product has two different sources of the same data or information, but it uses the source that has less support for verification, is less trusted, or is less resistant to attack.