avast! 4 Linux Home Edition 1.0.5 allows local users to modify permissions of arbitrary files via a symlink attack on the /tmp/_avast4_ temporary directory.
http://www.vupen.com/english/advisories/2006/1387
http://www.securityfocus.com/archive/1/431019/100/0/threaded
http://securityreason.com/securityalert/764