Passwordless and keyless SSH guest access

Question

I am trying to set up a guest user that allows ssh access without a password AND without a keyfile.

All my searches turns up people trying to set up password-less entry with a keyfile. This is not what I'm looking for.

I would settle for just having a blank password, but I can't get that working either; if I delete the user's password, the SSH daemon won't allow any access. I've set "PermitEmptyPasswords yes" in the config file and restarted the service.

I'm running Ubuntu 14.04.1 LTS.

Answer 1

What you're looking for is anonymous SSH access. I found an article for SFTP, which applies to SSH too, if you leave out SFTP-specific stuff:

1. Create a new user:

   adduser --disabled-password anonymous
   

2. Make the password actually empty:

   sed -i -re 's/^anonymous:[^:]+:/anonymous::/' /etc/passwd /etc/shadow
   

3. Allow blank passwords for SSH sessions in PAM: edit /etc/pam.d/sshd and replace the line that reads @include common-auth with:

   auth [success=1 default=ignore] pam_unix.so nullok
   auth requisite pam_deny.so
   auth required pam_permit.so
   

4. Allow blank passwords for SSH sessions of anonymous in /etc/ssh/sshd_config:

   Match user anonymous
       PermitEmptyPasswords yes
   

5. Restart sshd:

   systemctl reload ssh.service
   

I didn't try it myself, but it looks plausible, since my first thought for the culprit was PAM.