The Metasync plugin for WordPress is vulnerable to unauthorized modification of data due to a missing capability check on the save_instant_indexing_settings() function in versions up to, and including, 2.6.23. This function is registered on the admin_init hook and only checks for the presence of $_POST['submit'] before writing attacker-supplied $_POST['metasync_post_types'] into the site-wide 'metasync_options_instant_indexing' option via update_option(); no current_user_can()/current_user_has_plugin_access() check and no nonce verification are performed. This makes it possible for authenticated attackers, with Subscriber-level access and above, to modify the site's Google Instant Indexing post-type configuration, controlling which post types are auto-submitted to Google's Instant Indexing service.