That's not really true. An unprivileged user shouldn't be able to take down a production system, or really adversely effect other users. Assuming you have disk quotas enabled, what else could an unprivileged user do?
Why do these people have shell access to production systems in the first place?
I have access to this box and it has granted me access to some other system which has useful data, like a database, NFS mount, or S3 bucket. Let me hop in here and grep for something juicy to steal, maybe flip some bits around to fuck with people, or just delete shit.
You can't steal data unless if you intentionally delete the original after copying, but then that is not really theft as any proper organisation will have backups.
"Theft" is a nice easy word for making a copy of data that you do not have permission to access.
How about deleting everything under /var/www/?
> >Plus, there's still a lot of damage you can do without root access.
> That's not really true. An unprivileged user
We can see that "unprivileged user" equals to anything that is not root in your post. Considering that definition www-data is an unprivileged user which can delete everything under /var/www/.
So no, what you are saying is not really true.
Obviously a user can modify their own files. The idea is if you compromise unprivileged user "scott", with their account, you can't harm other users or the system itself.
[1]easily. Technically it depends, but a hardened configuration would only give www-data permissions to read files its data files in /var/www, not write them (which includes delete), apart from things it actually needs to write like its app logs (and even then you should be using syslog facilities, which only let you write, again not delete or cause any issues). Principal of least privilege and all that. For fun, try to figure out how to ssh into your system as www-data and see the half dozen different roadblocks that come up in your way.