Possible Exploit?

I been getting hammered with the following from places all over the world. They are using the exact same link. After about 20 rapid hits, the site goes down because it runs out of memory.
The link is always the same: (website.org replaces my site)

https://website.org/?email_id=722&user_id=1818&controller=stats&action=analyse&wysija-page=1&render=1&wysijap=subscriptions

They always use 722 and 1818.