Ubuntu Server has a very large number of users in the OS. And after all vsftpd through these users becomes authorized. Not dangerous?

Question

System administration

Can't attackers log into FTP using one of them and still know what the password will be (or there will be no password at all)?
Or in ftp, in principle, can only root be of these?
Here is a screenshot of all users:

Answer 1

Study the documentation for the service you are interested in, moreover, the config itself for this service is well commented.
Hint ftpusers, user_list, userlist_deny

Answer 2

These are system users, they do not have a password. Try to log in under them - and you will see :)

Answer 3

These are system users and they do not have a password.
man adduser
on system user
The new system user has the /bin/false shell (if no --shell option is specified) and a locked password. Initial settings files are not copied.
If you are planning on many users who should not have access to the system, then consider creating virtual users.