iPhone Jailbreak Worries Security Experts

The recent arrival of a Web-based way to install software not approved by Apple on the iPhone, just after the Library of Congress sanctioned the practice, seemed as if it might make jailbreaking a mainstream activity.

But the scheme's reliance on a security flaw in the PDF code used in mobile Safari and a kernel vulnerability has prompted security experts to rethink their position on jailbreaking.

McAfee Avert Labs security research and communications manager David Marcus says that he uses a jailbroken iPhone for the security and command-line software that's not available in Apple"s iTunes App Store. He welcomed the Library of Congress' decision to allow jailbreaking as fair use and was looking forward to a Web-based jailbreaking mechanism.

His enthusiasm, however, has diminished, he said.

"I hope I am not the only one who is bothered by this because it begs the question 'What else can this be used for?'" he wrote in a blog post. "Vulnerabilities with reliable exploit code tend to get reused and repurposed for other attacks/malware/uses."

Marcus argues that this should serve as a wake-up call for mobile device users that remote exploitation represents a real risk.

Security firm F-Secure states the problem more succinctly: "If the vulnerability can be used to jailbreak, it can also be used for more malicious drive-by exploits."

The company notes that there have been four previously patched iOS CoreGraphics/PDF-related vulnerabilities and that WebKit and Safari account for 64% of iOS's security fixes.

F-Secure also says that the PDF exploit code crashes Foxit on Windows.

While security experts may find it difficult to endorse jailbreaking when it relies on exploit code, they're still able to appreciate the programming challenge.

"Very beautiful work," observed Charlie Miller, principal analyst for Independent Security Evaluators in a tweet. "Scary how it totally defeats Apple's security architecture."

Update: Changed "Adobe's PDF code" to "the PDF code used in mobile Safari" as PDF is an open standard and it's not clear whether Adobe, Apple or another party wrote the code.

Also, F-Secure has since published a correction: "Due to a communication error between our labs, we incorrectly stated that the exploit PDF files, mentioned below, crash Adobe Reader. This is not the case. Our apologies for the error."