The WP Fastest Cache plugin for WordPress versions up to and including 1.5.3 improperly caches the response of wp-activate.php, exposing sensitive information. This caching ignores no-store/no-cache headers, relevant cookies, and installation state, resulting in publicly accessible cache files containing plaintext credentials of the most recently activated Multisite user. Exploitation requires a Multisite subdirectory setup with public user and site registration enabled and only occurs after a legitimate user activates their account.