CVE 2008-5104
Ubuntu 6.06 LTS, 7.10, 8.04 LTS, and 8.10, when installed as a virtual machine by (1) python-vm-builder or (2) ubuntu-vm-builder in VMBuilder 0.9 in Ubuntu 8.10, have ! (exclamation point) as the default root password, which allows attackers to bypass intended login restrictions.
See the 
CVE page on Mitre.org
for more details.
