The Bookero.pl – system rezerwacji online plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the `bookero_products` shortcode's `hide_products` (and `filter_products`) attributes in versions up to and including 2.2. This is due to insufficient input sanitization and output escaping in the `bookero_products()` function — the raw attribute value is concatenated directly into an inline `<script>` block without any escaping. This makes it possible for authenticated attackers with contributor-level access and above to inject arbitrary web scripts into pages that will execute whenever a user accesses the injected page.