The Custom Field Suite plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'cfs[fields][*][name]' parameter in all versions up to, and including, 2.6.5 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, with administrator-level access, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. This only affects multi-site installations and installations where unfiltered_html has been disabled.