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White hat warns against iPhone SMS spoofing bug

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Security researchers have discovered an iPhone bug that allows for spoofed SMSes with bogus return addresses to be sent to fanbois.

The bug creates a means for interested parties to send SMS messages to affected handsets that appear to come from any (arbitrary) number that the sender specifies. The issue specifically affects iPhone-fondlers because of the way Apple's iOS handles the User Data Header component of SMS text messages, which defines advanced features only used in smartphones. Specifically, iPhones don’t display the phone number of the indivdual who sent you a message, just whatever name they choose to type in.

Using the flaw, an attacker might be used to spoof messages from either banks or credit card firms, perhaps inviting potential marks to visit websites under the control of hackers. As such it poses a phishing risk, especially with the increased use of mobile banking, to say nothing about the use of text messages to mobiles for out-of-band online banking authentication.

Pod2g, the white hat security researcher who discovered the bug, said the flaw has existed since the beginning of the implementation of SMS in the iPhone, and is still there in iOS 6 beta 4.

In a blog post, Pod2g explains the impact of the bug.

"In the text payload, a section called UDH (User Data Header) is optional but defines lot of advanced features not all mobiles are compatible with. One of these options enables the user to change the reply address of the text. If the destination mobile is compatible with it, and if the receiver tries to answer to the text, he will not respond to the original number, but to the specified one.

"Most carriers don't check this part of the message, which means one can write whatever he wants in this section: a special number like 911, or the number of somebody else. In a good implementation of this feature, the receiver would see the original phone number and the reply-to one. On iPhone, when you see the message, it seems to come from the reply-to number, and you lose track of the origin."

Pod2g is calling on Apple to fix the flaw before releasing the final version of iOS 6.

Apple urged customers to be wary of spoofed SMS messages.

"Apple takes security very seriously," the firm said in a statement, PC World reports. "When using iMessage instead of SMS, addresses are verified which protects against these kinds of spoofing attacks.

"One of the limitations of SMS is that it allows messages to be sent with spoofed addresses to any phone, so we urge customers to be extremely careful if they're directed to an unknown website or address over SMS," it adds. iMessage is Apple's encrypted instant messaging service. ®

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