pam_console PAM module in Linux systems allows a user to access the system console and reboot the system when a display manager such as gdm or kdm has XDMCP enabled.
https://exchange.xforce.ibmcloud.com/vulnerabilities/5001
http://www.redhat.com/support/errata/RHSA-2000-044.html
http://archives.neohapsis.com/archives/bugtraq/2000-07/0455.html
http://archives.neohapsis.com/archives/bugtraq/2000-07/0398.html