Gwolle Guestbook <= 1.5.3 is vulnerable to Remote File Inclusion

PHP remote file inclusion vulnerability in the Gwolle Guestbook plugin before 1.5.4 for WordPress, when allow_url_include is enabled, allows remote authenticated users to execute arbitrary PHP code via a URL in the abspath parameter to frontend/captcha/ajaxresponse.php. NOTE: this can also be leveraged to include and execute arbitrary local files via directory traversal sequences regardless of whether allow_url_include is enabled.