The Meta Box – A Framework for Dynamic Websites plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'profile_background[<attacker-chosen key>]' parameter in all versions up to, and including, 5.15.2 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. Exploitability depends on a consuming plugin or theme built on Meta Box that exposes the background field to lower-privileged users and renders stored values via the rwmb_the_value()/format_single_value() pattern; the effective minimum privilege is whatever role that consumer permits, demonstrated at Subscriber level.