The (1) python-vm-builder and (2) ubuntu-vm-builder implementations in VMBuilder 0.9 in Ubuntu 8.10 omit the -e option when invoking chpasswd with a root:! argument, which configures the root account with a cleartext password of ! (exclamation point) and allows attackers to bypass intended login restrictions.
https://exchange.xforce.ibmcloud.com/vulnerabilities/46603
https://bugs.launchpad.net/ubuntu/+source/vm-builder/+bug/296841
http://www.ubuntu.com/usn/usn-670-1
http://www.securityfocus.com/bid/32292