Comment 27 for bug 1569237

Ok, I confirm the problem is still present for version: 20161014.0.0

Concerning workarounds you can set:

# SSH options.
    config.ssh.insert_key = true
    config.ssh.forward_agent = true

which will copy your public ssh key in the "ubuntu" account. You'll be then able to login using
vagrant ssh

If you want you can also set a password during your provision phase (I've tested with a shell provision), or make sure that your user is listed in the sudoers users. @ruijing-guo Having the source code for the box would indeed help fixing the issue!

Denis