passwd in Directory Services in Mac OS X 10.3.x before 10.3.9 and 10.4.x before 10.4.5 allows local users to overwrite arbitrary files via a symlink attack on the .pwtmp.[PID] temporary file.
https://exchange.xforce.ibmcloud.com/vulnerabilities/25274
http://www.vupen.com/english/advisories/2006/0791
http://www.us-cert.gov/cas/techalerts/TA06-062A.html
http://www.securityfocus.com/bid/16907
http://www.securityfocus.com/archive/1/426535/100/0/threaded
http://www.idefense.com/intelligence/vulnerabilities/display.php?id=400
http://secunia.com/advisories/19064
http://lists.apple.com/archives/security-announce/2006/Mar/msg00000.html