1. Log in as an administrator
2. Visit /wp-admin/admin.php?page=advance-search and create a new shortcode
3. In the "Post Type" section, fill the "List of Post Meta Keys" field with the following PoC:

', data=(SELECT sleep(10) FROM wp_users)-- a

4. Save the shortcode, and notice the requests takes a long time to finish, indicating our `sleep(10)` instruction executed in the context of an SQL query.