Preface: Computer technology especially software application is the soul of digital world.
Background: Pingbacks (also known as trackbacks) are a form of automated comment for a page or post, created when another WordPress blog links to that page or post. When you publish a new blog post, WordPress attempts to ‘ping‘ all the sites that were linked to in your post. i.e. Your WordPress website is informing other websites that you’ve linked to them.
Design weakness: Trackbacks and Pingbacks were meant to help inter-blog conversation when the specification was created years ago. These days almost 100% of Trackbacks and Pingbacks are spam, said Akismet. May cause more trouble!
Comments: WordPress release ver 5.3.1 on December 2019. However above concerns seem not been addressed in the moment. Heard that attacker can exploit the weakness of pingback. And work together with XML-RPC. As a result, it will consume system resources causes a denial of service. So we must staying alert!
Remedy: Refer to diagram
5.3.1 Official announcement – https://wordpress.org/support/wordpress-version/version-5-3-1/