pam_wheel in Linux-PAM 0.78, with the trust option enabled and the use_uid option disabled, allows local users to spoof log entries and gain privileges by causing getlogin() to return a spoofed user name.
https://euvd.enisa.europa.eu/vulnerability/EUVD-2003-0382
http://www.redhat.com/support/errata/RHSA-2004-304.html