FTP access to server subdirectory = root?

Question

FTP

Once I was a victim of Chinese hackers (they hacked a server through an outdated phpmailer - a vulnerability through the 5th sendmail parameter), I thought, how can I now safely give someone ftp access to a particular server directory? After all, an attacker can upload a backdoor there in no time and get root, or am I wrong?

Answer 1

By uploading it to the "backdoor" folder, the alleged attacker will be able to run any scripts on behalf of the web server. Well, or on behalf of php-fpm, for example. Shell scripts will run under the same name. Therefore, "getting root" is not possible by default.
The presence of chroot in ftp, in its essence, destroys the described problem in the bud.
BUT! All of the above is true in the absence of an exploit of critical kernel vulnerabilities. Therefore, if there are current security updates.