The HFS+ file system does not apply strict privilege rules during the creating of hard links. The ability to create hard links to directories is wrong implemented and such an issue is affecting OS versions greater or equal to 10.5. The vulnerability allows creating a large number of hard links to directories, potentially leading to a kernel crash when certain commands like 'ls' or 'find' are executed. The exploit code can be found at http://cert.cx/stuff/l2.c.