Leopard security bug puts Mail users at risk

Programmers have reintroduced a yawning security hole in Leopard, the latest version of Apple's highly regarded operating system, after having patched it more than 20 months ago in an earlier version, a researcher has warned.

The bug in Apple Mail makes it possible for attackers to run malicious code on a victim's machine by disguising an executable program as an image or other type of innocuous file, said Juergen Schmidt, editor-in-chief at Heise Security. A user can become infected simply by clicking on an attachment that looks like a jpeg image.

The bug is similar, if not identical, to one that Apple patched in March 2006, which also affected the Safari browser and iChat instant messenger program. The fix prompted Tiger, Leopard's predecessor, to inspect attached files and present a warning if the file a user clicked on was potentially unsafe.

Alas, that warning has largely vanished when Leopard users click on disguised executable files received in Mail, said Schmidt, who has set up a demo exploiting the bug here. About 90 percent of the time, he said, the file will run with no warning. He has yet to pinpoint what causes the dialog box to appear sometimes and not others.

"You would think that since they went to the trouble to fix it in Tiger, why reintroduce it in Leopard?" said Kevin Long, a researcher at Verizon Business, who specializes in security issues affecting Apple software. "The fact that they had done that before in Tiger and they didn't pro actively put that in Leopard is unfortunate."

Apple representatives didn't respond to a request for comment by time of writing. Apple has sold more than 2 million copies of Leopard to date.

Shortcomings in file validation have plagued Apple for some time now. The original bug resided in Mac operating systems for years before Apple finally patched the vulnerability. Even then, the security measure was criticized by some because it didn't work with third-party apps such as Firefox or Thunderbird and because OS X still made it easy to disguise malicious files as images.

Schmidt says he has not yet analyzed Safari or iChat to see if they properly validate files under Leopard but says "it's entirely possible" they don't. ®