gnome-pty-helper in GNOME libzvt2 and libvte4 allows local users to spoof the logon hostname via a modified DISPLAY environment variable. NOTE: the severity of this issue has been disputed.
https://exchange.xforce.ibmcloud.com/vulnerabilities/22496
http://www.vupen.com/english/advisories/2005/1931
http://secunia.com/advisories/17023