Sniffer hijacks secure traffic from unpatched iPhones

Nine-year-old bug patched for newer iPhones, iPads, but older models "perpetually vulnerable," says expert

Almost anyone can snoop the secure data traffic of unpatched iPhones and iPads using a recently-revised tool, a researcher said today as he urged owners to apply Apple's latest iOS fix.

The nine-year-old bug was quashed Monday when Apple issued a patch for the iPhone 4, iPhone 3GS and third- and fourth-generation iPod Touch.

If those devices aren't patched, attackers can easily intercept and decrypt secure traffic -- the kind guarded by SSL, which is used by banks, e-tailers and other sites -- at a public Wi-Fi hotspot, said Chet Wisniewski, a security researcher with U.K.-based Sophos.

"This is a nine-year-old bug that Moxie Marlinspike disclosed in 2002," said Wisniewski in an interview today.

On Monday, Marlinspike released a revision of his long-available "sslsniff" traffic sniffing tool that allows a user to intercept SSL traffic from vulnerable iOS devices. "My mother could actually use this," said Wisniewski, alluding to the tool's simplicity.

The bug Apple patched was in the parsing of SSL certificates on iOS, according to Wisniewski and the researchers Apple credited with reporting the flaw.

"iOS's SSL certificate parsing contains a flaw where it fails to check the basicConstraints parameter of certificates in the chain," said Trustwave, a Chicago security firm, in a Monday advisory . "By signing a new certificate using a legitimate end entity certificate, an attacker can obtain a 'valid' certificate for any domain."

Apple credited Trustwave's Paul Kehrer and Recurity Lab's Gregor Kopf with reporting the vulnerability.

Wisniewski confirmed the bug by using a legitimate certificate for his own website to create a valid certificate for PayPal. If he had proceeded, he could have intercepted others' iOS-generated traffic to the real PayPal site and steal their usernames and passwords.

"Anybody can sign anything," said Wisniewski.

Marlinspike disclosed the underlying vulnerability in 2002 , and created sslsniff that same year as a proof-of-concept demonstration of a "man-in-the-middle" attack using rogue certificates. Microsoft patched the bug in Windows' cryptographic component in 2002, but Apple had overlooked it in iOS.

"It's probably been in [iOS] since day one," said Wisniewski, who speculated that even attackers hadn't known of the flaw. "Someone would likely would noticed if it had been used, because every Windows user would have been getting browser warnings [of an invalid certificate] on a public Wi-Fi network even as iPhone users were seeing no such warning."

On Monday Marlinspike refreshed sslsniff to give it the ability to parse SSL traffic from iOS devices. Anyone who downloads the tool can then intercept secured data traffic from unpatched iPhones, iPads and iPod Touches.

"This is worse than Firesheep, because [sslsniff] lets anyone see anything that uses SSL," said Wisniewski, talking about the Firefox add-on that caused a stir last year.

Firesheep let anyone able to launch a browser hijack others' access to Facebook, Twitter and a handful of other services. It was downloaded hundreds of thousands of times as media reports widely circulated last October.

Although a patch for the certificate bug is available for some iPhone and iPod Touch owners, not everyone can protect themselves, Wisniewski said, because Apple has stopped supporting older devices with security and iOS updates.

People with an original iPhone, iPhone 3G, or first- or second-generation iPod Touch cannot patch their devices, for instance.

That prompted Wisniewski to warn users of those models, and people with a newer iOS device that hasn't been patched, against accessing SSL-protected sites and services, especially when they're connected to the Internet via a public wireless network.

"If you are using an iPod Touch generation one or two, or an iPhone older than the 3GS, you will be perpetually vulnerable," Wisniewski said in a blog posted late Monday. "Owners of these devices should not use them for any purpose for which security or privacy is required."

And until users patch newer iOS devices, they should "use their device [only] for telephone calls," Wisniewski added.

Recurity has created a test site that shows whether an iPhone, iPad or iPod Touch is vulnerable to the man-in-the-middle attacks.

Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer, on Google+ or subscribe to Gregg's RSS feed. His e-mail address is gkeizer@computerworld.com.

See more articles by Gregg Keizer.

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