The Multi Functional Flexi Lightbox plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the arv_lb[message] parameter in all versions up to, and including, 1.2 due to insufficient input sanitization and output escaping. This is due to the arv_lb_options_val() sanitize callback returning user input without any sanitization, and the stored message value being output in the genLB() function without 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 a page or post with the lightbox enabled.