The Click to Chat plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the ‘data-no_number’ parameter in all versions up to, and including, 4.22 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.
https://wordpress.org/plugins/click-to-chat-for-whatsapp/#developers