Vagrant “Timed out while waiting for the machine t

I had a previously working setup with vagrant 1.8.1 and virtualbox 5.0.22, but after upgrading to vagrant 1.8.5 and 5.1.0, i now get the dreaded "Timed out while waiting for the machine to boot."

Any options other than downgrading?

Full output:

Bringing machine 'centos7' up with 'virtualbox' provider...
==> centos7: Importing base box 'centos/7'...
==> centos7: Matching MAC address for NAT networking...
==> centos7: Checking if box 'centos/7' is up to date...
==> centos7: Setting the name of the VM: centos7-openvpn
==> centos7: Clearing any previously set network interfaces...
==> centos7: Preparing network interfaces based on configuration...
    centos7: Adapter 1: nat
    centos7: Adapter 2: bridged
==> centos7: Forwarding ports...
    centos7: 22 (guest) => 2222 (host) (adapter 1)
==> centos7: Running 'pre-boot' VM customizations...
==> centos7: Booting VM...
==> centos7: Waiting for machine to boot. This may take a few minutes...
    centos7: SSH address: 127.0.0.1:2222
    centos7: SSH username: vagrant
    centos7: SSH auth method: private key
    centos7: Warning: Remote connection disconnect. Retrying...
    centos7:
    centos7: Vagrant insecure key detected. Vagrant will automatically replace
    centos7: this with a newly generated keypair for better security.
    centos7:
    centos7: Inserting generated public key within guest...
    centos7: Removing insecure key from the guest if it's present...
    centos7: Key inserted! Disconnecting and reconnecting using new SSH key...
    centos7: Warning: Authentication failure. Retrying...
    centos7: Warning: Authentication failure. Retrying...
    centos7: Warning: Authentication failure. Retrying...
    centos7: Warning: Authentication failure. Retrying...
    centos7: Warning: Authentication failure. Retrying...
    centos7: Warning: Authentication failure. Retrying...
    centos7: Warning: Authentication failure. Retrying...
    centos7: Warning: Authentication failure. Retrying...
    centos7: Warning: Authentication failure. Retrying...
    centos7: Warning: Authentication failure. Retrying...
    centos7: Warning: Authentication failure. Retrying...
    centos7: Warning: Authentication failure. Retrying...
    centos7: Warning: Authentication failure. Retrying...
    centos7: Warning: Authentication failure. Retrying...
    centos7: Warning: Authentication failure. Retrying...
    centos7: Warning: Authentication failure. Retrying...
    centos7: Warning: Authentication failure. Retrying...
    centos7: Warning: Authentication failure. Retrying...
    centos7: Warning: Authentication failure. Retrying...
    centos7: Warning: Authentication failure. Retrying...
    centos7: Warning: Authentication failure. Retrying...
    centos7: Warning: Authentication failure. Retrying...
    centos7: Warning: Authentication failure. Retrying...
    centos7: Warning: Authentication failure. Retrying...
    centos7: Warning: Authentication failure. Retrying...
    centos7: Warning: Authentication failure. Retrying...
    centos7: Warning: Authentication failure. Retrying...
Timed out while waiting for the machine to boot. This means that
Vagrant was unable to communicate with the guest machine within
the configured ("config.vm.boot_timeout" value) time period.

If you look above, you should be able to see the error(s) that
Vagrant had when attempting to connect to the machine. These errors
are usually good hints as to what may be wrong.

If you're using a custom box, make sure that networking is properly
working and you're able to connect to the machine. It is a common
problem that networking isn't setup properly in these boxes.
Verify that authentication configurations are also setup properly,
as well.

If the box appears to be booting properly, you may want to increase
the timeout ("config.vm.boot_timeout") value.

This is caused by bug #7610 which is already fixed in git.

You can apply the fix yourself while you wait for a new release by editing the file vagrant/plugins/guests/linux/cap/public_key.rb and appliying the following change which is described in the bug report:

diff -uNr vagrant-original/plugins/guests/linux/cap/public_key.rb vagrant/plugins/guests/linux/cap/public_key.rb
--- vagrant-original/plugins/guests/linux/cap/public_key.rb     2016-07-19 12:06:56.575045974 -0500
+++ vagrant/plugins/guests/linux/cap/public_key.rb      2016-07-19 12:07:34.303376009 -0500
@@ -54,6 +54,7 @@
             if test -f ~/.ssh/authorized_keys; then
               grep -v -x -f '#{remote_path}' ~/.ssh/authorized_keys > ~/.ssh/authorized_keys.tmp
               mv ~/.ssh/authorized_keys.tmp ~/.ssh/authorized_keys
+              chmod 0600 ~/.ssh/authorized_keys
             fi

             rm -f '#{remote_path}'