bbp style pack <= 6.4.5 - Authenticated (Subscriber+) Stored Cross-Site Scripting via Topic Form Additional Fields

Summary

The bbp Style Pack plugin for WordPress is vulnerable to Stored Cross-Site Scripting in versions up to, and including, 6.4.5 via the Topic Form Additional Fields feature. This is due to insufficient input sanitization in bsp_topic_fields_form_save() (which writes $_POST['bsp_topic_fields_label{n}'] directly to post meta via update_post_meta() with no filtering) and missing output escaping in bsp_topic_content_append_topic_fields() (which concatenates the stored meta value into an HTML <span> and echoes it via apply_filters/echo without esc_html()). This makes it possible for authenticated attackers, with Subscriber-level access and above (who have bbPress topic-creation privileges), to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page, including unauthenticated visitors.