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Researchers from Purdue University and the University of Iowa have identified a flaw in the implementation of 4G and 5G mobile networks that could enable an attacker to steal a smartphone’s identity.
In their paper Privacy attacks to the 4G and 5G cellular paging protocols using side channel information, the researchers described how they created a proof-of-concept attack called ToRPEDO (TRacking via Paging mEssage DistributiOn), which used low-cost hardware and software.
“All of our attacks have been validated in a realistic setting for 4G using cheap software-defined radio and open source protocol stack,” said the researchers.
According to the researchers, the attack relies on a weakness in the paging protocol that a 4G or 5G network uses to wake up a smartphone. The protocol is used to wake up the mobile when there is an incoming call, SMS or a message or update via messaging apps.
“In cellular networks, when a device is not actively communicating with a base station, it enters an idle, low-energy mode to conserve battery power,” the researchers wrote in the paper. “When there is a phone call or an SMS message, it needs to be notified. This is achieved by the paging protocol.”
The paging protocol assigns a random temporary mobile subscriber identity (TMSI), and the researchers found that because the TMSI is changed infrequently, it is possible for an attacker to learn exactly when a device wakes up to check for paging messages and to discover the device’s geographical location.
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The researchers also said that ToRPEDO enables an attacker with knowledge of the victim’s phone number to retrieve the international mobile subscriber identity (IMSI) by launching a brute-force attack.
They said a ToRPEDO-based attack relies on the ability to send multiple messages or phone calls to a targeted device. These messages can be sent discreetly, so the user is unaware that the attack is taking place.
However, the researchers noted: “For ToRPEDO to be successful, an attacker needs to have a network sniffer device in the same cellular area as the victim. If the number of possible locations that the victim can be in is large, the expense of installing sniffers ($200 each) could be an impediment to carrying out a successful attack.”