Security oversights by Mac developers and Apple allow users to pirate or modify applications downloaded from the Mac App Store, several users reported on Jan. 6.
Less than 24 hours after Apple unveiled the Mac App Store for the Mac OS X, reports emerged on various user forums, including Pastebin and Daring Fireball, that some paid apps do not properly validate App Store receipts, making it easy to obtain those programs for free.
Users can copy the App Store receipt from any legitimate Mac App Store download-free or paid-and paste it to validate other paid applications, according to the posted instructions.
"This isn't true for all paid Mac App Store apps," wrote John Gruber of Daring Fireball, but only for those applications with which developers were lax about applying Apple's recommendations on validating store receipts. The app checks to ensure there is a valid receipt, but it doesn't check that the ID listed on the receipt belongs to the app.
Just how many developers and apps didn't implement receipt validation correctly is unclear at this time, but the popular Angry Birds game happens to be one of them.
The lack of proper receipt validation makes it easier for users to pirate Mac App Store applications, and it seems inevitable that they will become readily available. "Someone who claims to provide you with paid applications for free may not simply give you a free program, they may give you an unwanted infection," said Sophos security researcher Chester Wisniewski on the Naked Security blog.
While this means Apple and Mac App Store developers miss out on legitimate revenue because of piracy, what's more worrying is the fact that many validations appear to have been skipped, said Wisniewski. Other than receipt checking, some developers neglected to perform other checks that open their apps to the possibility of being modified, he said.
Wisniewski found that some applications could be modified to include other executables, tricking users into running something other than what they expected. In his video example, Wisniewski showed how easily he could swap out the Angry Birds executable with the Firefox code. From the user's standpoint, it looked like Angry Birds, and the OS thought it was running Angry Birds. But when executed, it opened up Firefox.
"It wouldn't surprise me to see a surge in markets for pirated applications that might just be booby-trapped to include unexpected surprises," Wisniewski said.
Every program in the Mac App Store is reviewed by Apple and must pass a series of tests before it is accepted in the store. Gruber said it is surprising that Apple hadn't tested for something as basic as receipt validation before approving the apps.
Apple said that there were more than 1 million downloads from the Mac App Store on its first day. It was not clear what the breakdown was for paid and free apps.
If that isn't enough to give Apple a headache, Gizmodo reports that a group known as Hackulous has developed a program called Kickback, which claims to break the protection on any Mac App Store application, but that it will not release it until next month. "We're not going to release Kickback until well after the store's been established, well after developers have gotten their applications up," the group's spokesperson, "Dissident," told Gizmodo.
Hackulous has previously cracked the iPhone and iPad.