The media is already full of fear-mongering about “hackers,” so I want to point out that this particular vulnerability is unlikely to negatively affect you. But, that doesn’t mean it isn’t important to expose. Whenever your cell phone is on, it’s sending pings to the nearest cell towers. An IMSI-catcher is essentially a spoofed cell phone tower that black hat hackers can use to intercept those pings, and a simple ISMI-catcher can be built for as little as $20.
Every cell phone SIM card has a unique IMSI number, which identifies the device when it pings a cell tower. Police can subpoena records of those pings to determine if a suspect was in a given area at a particular time, and black hat hackers can do the same thing with an IMSI-catcher. On its own, there isn’t much they can do with that information. However, it can be used as the basis for more involved attacks to intercept and redirect text messages and phone calls, which is a far more serious threat that potentially puts your personal information at risk.
Joseph Cox of Vice’s Motherboard wanted to demonstrate just how inexpensive and easy a IMSI-catcher is to build. Doing so is as simple as buying a software-defined radio, in this case a NooElec NESDR Mini that costs just $20 on Amazon. Plug that into a laptop and install some readily-available open source software, and you’ve got yourself an IMSI-catcher. Cox only set this up to read IMSI numbers in the immediate area, but it could theoretically be used for much more. Unfortunately, there isn’t much you can do to protect yourself from this kind of attack, as it’s an issue on the infrastructure level.