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

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 'gamipress_achievement' 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. WordPress save-time wp_kses_post does not neutralize this payload because the injected value is stored inside a shortcode attribute rather than as a raw HTML tag, and is only emitted into HTML at render time without escaping.