A security researcher has discovered a “severe flaw” in iOS that could allow hackers to spoof SMS messages. The researcher, who calls himself “pod2g,” said in a blog postFriday that the problem has existed since the iPhone first supported SMS messaging.
If you either own a smartphone, or a modem and an account in a SMS gateway, you can send texts in raw PDU format (some services also exist to send a text with an HTTP request in raw PDU format). For the easiest smartphone option, there are different tools available online. I made one for the iPhone 4 that I will publicize soon.
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 loose track of the origin.
Why is it an issue ?
- pirates could send a message that seems to come from the bank of the receiver asking for some private information, or inviting them to go to a dedicated website. [Phishing]
- one could send a spoofed message to your device and use it as a false evidence.
- anything you can imagine that could be utilized to manipulate people, letting them trust somebody or some organization texted them.
Pod2g is calling on Apple to fix the issue.