The WP Statistics plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'utm_source' parameter in all versions up to, and including, 14.16.4. This is due to insufficient input sanitization and output escaping. The plugin's referral parser copies the raw utm_source value into the source_name field when a wildcard channel domain matches, and the chart renderer later inserts this value into legend markup via innerHTML without escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in admin pages that will execute whenever an administrator accesses the Referrals Overview or Social Media analytics pages.