EmailKit <= 1.6.5 - Authenticated (Author+) Arbitrary File Read via 'emailkit-editor-template' REST Parameter

The EmailKit plugin for WordPress is vulnerable to Arbitrary File Read in all versions up to and including 1.6.5. This is due to a flawed path traversal validation in the create_template() method of the CheckForm class, where realpath() is called on the allowed base directory (wp-content/uploads/emailkit/templates/) which may not exist, causing it to return false. In PHP 8.x, strpos($real_path, false) implicitly converts false to an empty string, and strpos() with an empty needle always returns 0, causing the check strpos(...) !== 0 to evaluate to false and bypassing the path validation entirely. This makes it possible for authenticated attackers, with Author-level access and above, to read arbitrary files from the server, including sensitive files such as wp-config.php, by supplying an absolute path to the emailkit-editor-template REST API parameter.