While 4G LTE provides for a level of privacy for cellular customers through the use of ephemeral “subscriber identities” over the air,
researchers at the Korea Advanced Institute of Science and Technology recently found that the Globally Unique Temporary Identifier (GUTI) issued by a majority of 4G LTE carriers was far from temporary. While carriers do change the GUTI for phones periodically, the KAIST researchers found that 19 of the 28 carriers they surveyed did so in a very predictable way—making it easy to predict not only when a new ID would be assigned but also what most of the new GUTI would be, because much of it went unchanged.
“In our global-scale measurement analysis, we did not find a single carrier that implemented GUTI reallocation securely,” the KAIST researchers wrote. A similar problem exists in 3G GSM networks’ temporary subscriber IDs.
The exploits discovered by the Purdue/Iowa team go beyond simple location tracking. One exploit allows tracking of a target by just using a phone number, sending a phone call while simultaneously blocking call notification by hijacking the target’s paging network connection. Another attack allows a malicious device to pose as the target device through an “authentication relay” attack before sending its own location data and other messages to distort carrier location data logs.
The paging network, which also carries SMS and other messages, can be hijacked for other purposes: to send messages to the network posing as the target, inject fake emergency alert messages, quietly kick the victim off the cellular network, or conduct denial-of-service and power depletion attacks against the victim.