Sudo asking for password even though user doesn’t have a password set

sudo requires a password by default on Mac OS X.

Apple's knowledge base article explains more, Mac OS X: sudo command requires a non-blank admin password:

In Mac OS X v10.5 through 10.5.8, if you press the Return key at the password prompt without entering a password (even if the user has no password, which is not recommended), the command entered will not execute and you will be returned to a command prompt.

In Mac OS X v10.6 or later, if you press the Return key at the password prompt without entering a password, the message "Sorry, try again." will be displayed and you will be prompted for a password again.

If your administrator account has no password (a blank password), you must give that user a password before using the sudo command.

If you must remove the need for a password to use sudo, you can edit the /etc/sudoers file using visudo command. A thread on macoshints discusses how:

Use the visudo command as root.

Look for the line:

%admin ALL=(ALL) ALL

Change it to:

%admin ALL=(ALL) NOPASSWD: ALL

Requiring a password is highly recommended. Removing this check reduces the security of your Mac and exposes your computer to attack or abuse.

The group entry %admin ALL=(ALL) ALL seems to override the user specific entry. I found moving the user specific entry so that is appears after the group entry fixes this. Maybe sudo parses the entire file and it uses the last matching entry?

Changing your sudoers file to something similar to below should work.

# User privilege specification
root    ALL=(ALL) ALL
%admin  ALL=(ALL) ALL
howard  ALL=(ALL) NOPASSWD: ALL