updated 10:45 am EST, Wed November 21, 2007
Leopard quarantine bug
A flaw has surfaced in Apple's Leopard quarantine system that allows unsuspecting Mac users to open specially crafted files that run with nearly any application. The quarantine system included in the latest revision of Mac OS X is designed to alert users when they attempt to open applications or disk images that arrive via Mail, Safari, or iChat. However the safety measure fails to issue a proper warning when Mail attachments posing as pictures arrive containing a resource fork which instructs the Mac to open the file using a specific application.
A proof of concept exploit created by heiss Security -- the firm that discovered the bug -- demonstrates the flaw by printing some harmless text in a terminal window after the user clicks on an image received via email, noting that the shell script could just as easily contain commands to delete all of a user's files.
Intego's sample file using Apple's Mail program appears as an attachment with a JPEG icon that will open in Preview when double clicked, but attempting to view the file with Quick Look reveals the truth about the masked shell script. Users receiving such a file might click the attachment to view the contents, trusting Apple's quarantine security measure to warn them about any unwanted applications received by email or other means.
"Until this bug is corrected in Mac OS X 10.5, Mac users are at risk of receiving maliciously crafted files, pretending to be image files, which could delete all of a user's files, or may contain Trojan horses," Intego said. "It is important that users do not open attachments from unknown senders, especially those that come with spam messages."