O Vagrant lança a mensagem de erro:
==> default: Mounting NFS shared folders...
mount -o 'vers=3,udp' 192.168.33.1:'/home/xxx/vagrant/www' /home/www
mount.nfs: Operation not permitted
ssh para o convidado e corre
root@debian:~# mount -o 'vers=3,udp' 192.168.33.1:'/home/xxx/vagrant/www' /home/www -v
mount: no type was given - I'll assume nfs because of the colon
mount.nfs: timeout set for Tue Jul 15 22:26:56 2014
mount.nfs: trying text-based options 'vers=3,udp,addr=192.168.33.1'
mount.nfs: prog 100003, trying vers=3, prot=17
mount.nfs: trying 192.168.33.1 prog 100003 vers 3 prot UDP port 2049
mount.nfs: prog 100005, trying vers=3, prot=17
mount.nfs: trying 192.168.33.1 prog 100005 vers 3 prot UDP port 54188
mount.nfs: portmap query failed: RPC: Program/version mismatch
mount.nfs: Operation not permitted
mount.nfs: portmap query failed: RPC: Program/version mismatch
Poderia ser uma pista, mas não teve sorte com o googling. O host (servidor nfs) suporta nfs4 e nfs3.
Por favor, sinta-se à vontade para pedir mais informações.