The flaw involves the way OS X handles disk images and could be used to crash or take over a vulnerable machine.
So far the DMG bug has only been shown to work under laboratory conditions and has not been seen in the wild.
The DMG bug came to light during a month-long project run by the Info-Pull research group that aimed to find one "kernel" bug a day. The kernel is the heart of an operating system.
The warning from US Cert said the memory corruption caused by the bug could make a computer unstable or allow an attacker to hijack it. It urged users to avoid downloading DMG files, which bear a .dmg suffix, from unknown sources.