Blocksy Companion <= 1.8.67 is vulnerable to Cross Site Scripting (XSS) vulnerability

The Blocksy Companion plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the plugin's blocksy_posts shortcode in versions up to, and including, 1.8.67 due to insufficient input sanitization and output escaping on user supplied 'class' attribute. This makes it possible for authenticated attackers with contributor-level and above permissions to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.