The Scheduled Announcements Widget WordPress plugin before 1.0 does not validate and escape some of its shortcode attributes before outputting them back in a page/post where the shortcode is embed, which could allow users with the contributor role and above to perform Stored Cross-Site Scripting attacks.
https://wpscan.com/vulnerability/6d332a47-e96c-455b-9e8f-db6dbb59b518