The User Language Switch plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'tab_color_picker_language_switch' parameter in all versions up to, and including, 1.6.10 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, with administrator-level access and above, 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.