Ubuntu disables password based root login by default. That seems like it results in being able to boot into recovery and drop into a root shell without needing to provide a password, from where you can then give yourself access to the system.
Am I missing something or is that a vulnerability in the default install that allows you to bypass needing an account password?
/etc/passwd
file is not encrypted and you have physical access to the system or boot disk, you can always give yourself "root" access. – FedKad Jul 21 '21 at 08:34