The VikBooking Hotel Booking Engine & PMS plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'vbfX' parameter in all versions up to, and including, 1.8.13 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. The vbfX custom-field value is stored via the public-facing saveorder task, which has no capability or authentication check enforced by default, enabling fully unauthenticated submission of malicious payloads.