The WP-Matomo Integration (WP-Piwik) plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'wp-piwik' shortcode in versions up to, and including, 1.0.28 due to insufficient input sanitization and output escaping on user supplied attributes. 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.