A certain Ubuntu build procedure for perf, as distributed in the Linux kernel packages in Ubuntu 10.04 LTS, 12.04 LTS, 12.10, 13.04, and 13.10, sets the HOME environment variable to the ~buildd directory and consequently reads the system configuration file from the ~buildd directory, which allows local users to gain privileges by leveraging control over the buildd account.
https://lists.ubuntu.com/archives/kernel-team/2013-July/031249.html
https://lists.ubuntu.com/archives/kernel-team/2013-July/031248.html
https://launchpad.net/bugs/1206200
http://www.ubuntu.com/usn/USN-1947-1
http://www.ubuntu.com/usn/USN-1946-1
http://www.ubuntu.com/usn/USN-1945-1
http://www.ubuntu.com/usn/USN-1944-1
http://www.ubuntu.com/usn/USN-1943-1
http://www.ubuntu.com/usn/USN-1942-1
http://www.ubuntu.com/usn/USN-1941-1
http://www.ubuntu.com/usn/USN-1939-1
http://www.ubuntu.com/usn/USN-1938-1
http://people.canonical.com/~ubuntu-security/cve/2013/CVE-2013-1060.html