The Ubuntu 5.10 installer does not properly clear passwords from the installer log file (questions.dat), and leaves the log file with world-readable permissions, which allows local users to gain privileges.
https://launchpad.net/distros/ubuntu/+source/shadow/+bug/34606
https://exchange.xforce.ibmcloud.com/vulnerabilities/25170
https://euvd.enisa.europa.eu/vulnerability/EUVD-2006-1187
http://www.vupen.com/english/advisories/2006/0927
http://www.securityfocus.com/bid/17086