The base-files package before 5.0.0ubuntu7.1 on Ubuntu 9.10 and before 5.0.0ubuntu20.10.04.2 on Ubuntu 10.04 LTS, as shipped on Dell Latitude 2110 netbooks, does not require authentication for package installation, which allows remote archive servers and man-in-the-middle attackers to execute arbitrary code via a crafted package.
http://www.vupen.com/english/advisories/2010/2015
http://www.ubuntu.com/usn/usn-968-1