Avada (Fusion) Builder <= 3.15.6 - Authenticated (Contributor+) Stored Cross-Site Scripting via 'size' Shortcode Attribute

The Avada (Fusion) Builder plugin for WordPress is vulnerable to Stored Cross-Site Scripting via 'size' Shortcode Attribute in all versions up to, and including, 3.15.6 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's wp_kses_post filter does not neutralize the payload because the injected content resides entirely within a shortcode attribute string containing no HTML angle brackets, causing kses to pass it through unchanged at save time.