How can you mess with a landing page?

Question

PHP

Dear comrades, tell me,
I was visited by an interesting thought, which I cannot get rid of.

Let's say I have a landing page, html/php, without a database!
Is it possible to come up with some kind of loophole, make it so that the client can break it (in any sense =))))
....
while it came to my mind, prepare the function for creating a .txt file, and by GET request this file was filled and the text was displayed full page =))

What are your ideas.

Answer 1

What did the client do to you? Of course, you can leave the backdoor and then launch a virus there, but I didn’t tell you anything. Your idea is certainly interesting, but still doing something and spoiling your reputation is such an idea