The "Month of Kernel Bugs" project has found two unpatched security vulnerabilities in the way Mac OS X handles .dmg files.
The first vulnerability, rated "highly critical" by security-firm Secunia, can lead to privilege escalation, denial of service, and system access by a remote user (if Safari's open "safe" files option is checked).
The second issue is similar in nature, in that a corrupted UDTO HFS+ .dmg (ex. bad sectors) can lead to a denial of service condition.
A workaround for both issues is to disable Safari's option to open "safe" files after downloading, and to not open any .dmg file from a source you do not trust.
The latest findings increase the total to four security bugs found in Apple's software since the beginning of the project this month (See also: Airport Driver Exploit , fpathconf() Exploit ). The project has also targeted Windows, Linux, and other popular BSD distributions, with a stated goal to "check how many unreported and unknown issues can be found in kernel code out there, using simple, yet effective tools deploying techniques such as fuzzing and 'stress testing'."