The Ninja Forms - Excel Export plugin for WordPress is vulnerable to Stored Cross-Site Scripting in versions up to, and including, 3.3.6. This is due to the save_filter() AJAX handler storing the raw $_POST['filter'] array into a WordPress option via update_option() without any capability check, nonce verification, or input sanitization, combined with the get_filter_row() method on the admin Excel Export screen concatenating the stored filter values (field_key, condition, value) directly into HTML attributes without esc_attr(). This makes it possible for authenticated attackers, with subscriber-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.