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Updated The iOS 4 drive-by jailbreak released over the weekend uses a PDF exploit to weave its magic, according to an analysis by security researchers.

The hack, developed by the iPhone Dev Team and available via jailbreakme.com, can be run directly on a device running iOS 4. Earlier tools required a software download that was run via a computer paired with a targeted device - a far more convoluted route. The latest hack allows iPhones, iPads and iPod Touches running iOS 4 and iOS 4.01 to be jailbroken, after which users can install unapproved apps.

Mikko Hypponen, chief research officer at F-Secure, explained that the vulnerability stems from how mobile version of Safari handle PDF files and arises from a security bug in Apple's software.

"By default, there's no separate PDF viewer on an iPhone. Instead, PDF viewing is built into the Safari browser," Hypponen told El Reg. "The attack uses a corrupted font placed inside a PDF file to crash the Compact Font Format (CFF) handler."

"This is not an Adobe bug. It's an Apple bug," he added.

Analysis of the flaw is ongoing.

"It's unclear whether this has any implications on other platforms," Hypponen writes. "These files crash some PDF Readers on Windows, but that seems to be it."

F-Secure found that PDF files crashed both Adobe Reader and Foxit. The Finnish net security firm notes that the vulnerability used to jailbreak a device on one site might also be used for malicious drive-by exploits.

"While these files are not being used maliciously, an exploit is an exploit, and we'll add detections until we know more about the vulnerability," F-Secure adds.

The ease of jailbreaking iOS 4 devices using jailbreakme.com is illustrated by attempts to run the tool under the noses of Apple staff in one Apple Store, as shown in a picture here.

Naughty. ®

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