The Avalon23 Products Filter for WooCommerce plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'avalon23_qr' shortcode in all versions up to, and including, 1.1.6. This is due to insufficient input sanitization and output escaping on user-supplied shortcode attributes (notably 'title' and 'fixed_link') which are concatenated directly into single-quoted HTML attributes by the AVALON23_HELPER::draw_html_item() helper without esc_attr() or any other encoding. This makes it possible for authenticated attackers, with Contributor-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.