The Redux Framework plugin for WordPress is vulnerable to Stored Cross-Site Scripting via 'multi_media' Field Array Key in all versions 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. The wp_kses_post sanitization applied at save time operates only on array leaf values, leaving array keys entirely unsanitized; the injected key is then rendered directly into an id="filelist-<KEY>" HTML attribute without esc_attr() in Redux_Multi_Media::render(), allowing attribute breakout.