The Hydra Booking — Appointment Scheduling & Booking Calendar plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'first_name' parameter in all versions up to, and including, 1.2.2 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, with host-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. The tfhb_host role required to exploit this vulnerability can be self-assigned by any visitor via the plugin's public Signup shortcode, making this effectively exploitable by unauthenticated users who complete the registration flow.