How to set up Chmod on hosting to prevent sites from interacting with each other?

Question

Network administration

Gentlemen, brainy, please tell me how to set up Chmod so that sites do not affect each other on hosting. One old CMS was hacked and malicious scripts were also uploaded to other sites.
all sites are in separate folders in the root folder ... the hoster says that the web developer must configure the default chmod, we do not have such a ban..

Answer 1

each site must be run as its own user.
If you have shared hosting, then only add a separate user to each site, pay separately, etc.
If you have vds\vps\dedic - then start each site in a separate user.

Answer 2

Thanks for the answers , I think on this shared hosting it will not be possible to run each site on behalf of its user.