Attack coming from multiple IPs

I have an attack coming to a specific path repeatedly - every 10 minutes or so, the same exact address gets pinged.

I know this because I keep getting an error message in my Drupal logs about an attempt to access a page that does not exist.

sites/default/files/cache.php

How do I ban attempted connections to this address? I have IPtables enabled, I have various Drupal modules set to report and ban unusual traffic (but for some reason this gets through), and the file doesn't even exist.