There are security vulnerabilities in the phone-call routing protocol called SS7.
The flaws discovered by the German researchers are actually functions built into SS7 for other purposes—such as keeping calls connected as users speed down highways, switching from cell tower to cell tower—that hackers can repurpose for surveillance because of the lax security on the network.
Those skilled at the myriad functions built into SS7 can locate callers anywhere in the world, listen to calls as they happen or record hundreds of encrypted calls and texts at a time for later decryption. There also is potential to defraud users and cellular carriers by using SS7 functions, the researchers say.
The German researchers found two distinct ways to eavesdrop on calls using SS7 technology. In the first, commands sent over SS7 could be used to hijack a cell phone’s “forwarding” function—a service offered by many carriers. Hackers would redirect calls to themselves, for listening or recording, and then onward to the intended recipient of a call. Once that system was in place, the hackers could eavesdrop on all incoming and outgoing calls indefinitely, from anywhere in the world.
The second technique requires physical proximity but could be deployed on a much wider scale. Hackers would use radio antennas to collect all the calls and texts passing through the airwaves in an area. For calls or texts transmitted using strong encryption, such as is commonly used for advanced 3G connections, hackers could request through SS7 that each caller’s carrier release a temporary encryption key to unlock the communication after it has been recorded.
We’ll learn more when the researchers present their results.