GamiPress <= 7.9.9.1 - Authenticated (Contributor+) Stored Cross-Site Scripting via 'heading_size' Shortcode Attribute

The GamiPress – Gamification plugin to reward points, achievements, badges & ranks in WordPress plugin for WordPress is vulnerable to Stored Cross-Site Scripting via 'heading_size' Shortcode Attribute in all versions up to, and including, 7.9.9.1 due to insufficient input sanitization and output escaping. 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. The wp_kses_post filter applied at post save does not neutralize this payload because only the inert shortcode text is stored in post_content; the dangerous HTML is synthesized at render time by the shortcode handler, entirely bypassing save-time sanitization.