Certificate Assistant in Apple Mac OS X 10.5.6 allows local users to overwrite arbitrary files via unknown vectors related to an "insecure file operation" on a temporary file.
https://exchange.xforce.ibmcloud.com/vulnerabilities/48715
http://www.vupen.com/english/advisories/2009/0422
http://www.securityfocus.com/bid/33759
http://support.apple.com/kb/HT3438
http://securitytracker.com/alerts/2009/Feb/1021720.html
http://secunia.com/advisories/33937
http://lists.apple.com/archives/security-announce/2009/Feb/msg00000.html