First, not all attacks require to know the password. Many attacks against services (or daemons) target vulnerabilities in code and end in executing code on behalf of a user without knowing the password. In that case, the default
sudo configuration adds security by requiring the knowledge of the password.
Another example in a multi-user environment is when a user leaves his terminal unattended (you and I know that it is bad and never do it ourselves, but...) an attacker can execute commands on behalf of the user but still cannot use
Finally, as you speak of
ssh, the common use is to only use a (RSA) key for user authentication. That way, the
ssh connection never use the password, which is only used for a direct local connection or to gain root access via
sudo. It can even be forced by disabling the use of the password in
sshd configuration. In the case of a remote server, the local user password is then indeed only used to gain root access.
But the real answer to your question is the option does exist! The
/etc/sudoers file can be used to declare the boolean flag
rootpw. If this flag is set, the password shall be the password for root instead of the password for the current user.
sudoers contains the line:
then you will be asked for the root password. This flag is off by default and is seldom used because it is not really
sudo philosophy but
su one: if you do know the password for root, you can directly use
su by-passing all additional
sudo is indeed a highly versatile command, and you really should read