If this code is executed multiple times with the wrong PUK, the SIM card is locked permanently and the user needs to get a new one from the operator, Mulliner said.
Instead of using a "tel:" URI with the factory reset code in an iframe, an attacker could have ten iframes with the PIN changing code and wrong PUK on the malicious Web page .
Unlike the factory reset code which is supported only by certain devices from certain manufacturers, most Android phones should support the PIN changing code because it is standardized as a SIM card feature, Mulliner said. "The SIM issue is more problematic in my opinion."
Samsung has already fixed the USSD/MMI code execution issue for Galaxy S III devices. "We would like to assure customers that the recent security issue affecting the Galaxy S III has already been addressed in a software update," Samsung said Tuesday in a statement via email. "We believe this issue was isolated to early production devices, and devices currently available are not affected by this issue. To ensure customers are fully protected, Samsung advises checking for software updates through the 'Settings: About device: Software update' menu. We are in the process of evaluating other Galaxy models."
However, it's unlikely that all devices vulnerable to the SIM locking attack will receive firmware updates from their manufacturers. It's a known fact that most manufacturers are slow to issue firmware updates and many phone models are not even supported anymore so they will probably remain vulnerable.
Because of this, Mulliner created an application called TelStop that blocks the attack by registering a secondary "tel:" URI handler.
When TelStop is installed and the phone encounters a "tel:" URI, the user is presented with a dialog to choose between TelStop and the regular dialer. If TelStop is chosen, the application will reveal the content of the "tel:" URI and will display a warning if the content is likely to be malicious.
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