The WPBakery Page Builder plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'display_name / nickname' parameter in all versions up to, and including, 9.0.1 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, with subscriber-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. Successful execution requires that at least one public post attributed to the attacker's account be rendered through a Basic Grid using a Grid Builder template with the Post Author element configured to link to the post author; Author-level users can satisfy this precondition unassisted, while Subscribers depend on an administrator having assigned or published a post under their account.