wp-plain.php

I’m seeing a good deal of approved Forms with what looks like code being posted in my logs under the form WP-Plain.PHP. Which doesn’t exist or I’m getting a 404 error at least. I’m assuming this isn’t working or sending spam out but is it some type of 0-day vulnerability in WordPress? And is it possible to disallow the attempted page to an auto block of the IP?

The page I need help with: [log in to see the link]