The Planyo Online Reservation System plugin for WordPress is vulnerable to Server-Side Request Forgery leading to Local File Inclusion in all versions up to, and including, 3.0. The ulap.php file acts as an AJAX proxy and is directly accessible without WordPress bootstrapping or any authentication. The send_http_post() function validates the host of the provided URL against an allowlist that includes 'localhost', but critically fails to validate the URL scheme/protocol. This makes it possible for unauthenticated attackers to supply a file:// URL (e.g., file://localhost/etc/passwd) which bypasses the host allowlist check because parse_url() returns 'localhost' as the host. The URL is then passed to curl_init() or fopen(), both of which support the file:// protocol, allowing the attacker to read arbitrary local files on the server and have their contents returned in the HTTP response. This can lead to disclosure of sensitive files such as /etc/passwd, wp-config.php (containing database credentials and authentication keys), and other server-side files.