pam_motd (aka the MOTD module) in libpam-modules before 1.1.0-2ubuntu1.1 in PAM on Ubuntu 9.10 and libpam-modules before 1.1.1-2ubuntu5 in PAM on Ubuntu 10.04 LTS allows local users to change the ownership of arbitrary files via a symlink attack on .cache in a user's home directory, related to "user file stamps" and the motd.legal-notice file.
https://exchange.xforce.ibmcloud.com/vulnerabilities/60194
http://www.vupen.com/english/advisories/2010/1747
http://www.ubuntu.com/usn/USN-959-1
http://www.h-online.com/security/news/item/Ubuntu-closes-root-hole-1034618.html