Published: 7 July 2010
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.
From the Ubuntu security team
Denis Excoffier discovered that the PAM MOTD module in Ubuntu did not correctly handle path permissions when creating user file stamps. A local attacker could exploit this to gain root privilieges.