XNU 1228.9.59 and earlier on Apple Mac OS X 10.5.6 and earlier does not properly restrict interaction between user space and the HFS IOCTL handler, which allows local users to overwrite kernel memory and gain privileges by attaching an HFS+ disk image and performing certain steps involving HFS_GET_BOOT_INFO fcntl calls.

More... (http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2009-1235)