The Finder in Mac OS X and earlier allows local users to overwrite arbitrary files and gain privileges by creating a hard link from the .DS_Store file to an arbitrary file.
https://exchange.xforce.ibmcloud.com/vulnerabilities/19253
http://secunia.com/advisories/14188
http://marc.info/?l=bugtraq&m=110780124707975&w=2
http://lists.apple.com/archives/security-announce/2005/May/msg00001.html