While CSS is a broad term that includes devices that mimic legitimate mobile network towers to intercept cellular communications, IMSI catchers are the most common type of CSS that are used to capture the International Mobile Subscriber Identity (IMSI) of cellular devices.
Such tools differ in capability, with the StingRay family of IMSI catchers being one of the most notorious ones around. They are known to not only capture IMSI numbers to track cellular devices, but also intercept phone calls, text messages, and mobile internet traffic.
To combat these invasive tools, the Electronic Frontier Foundation (EFF) has launched a new open source tool designed to disrupt such covert surveillance tactics.
With an aim to fill the gaps in their knowledge of how CSS works, the Electronic Frontier Foundation has created the Rust-based Rayhunter, which runs on a Verizon Orbic Speed mobile hotspot device (Orbic RC400L).
Built to be easy to use, regardless of technical proficiency, when loaded on the Orbic device, Rayhunter constantly watches the communication between the mobile hotspot and the nearby connected cell tower, monitoring the traffic for any suspicious events.
For example, if the cell tower tries to downgrade the connection to the older, less secure 2G network or asks for the device's IMSI in a strange/unexpected way, then Rayhunter will flag these events and notify the user.
It does so by having a green line (or blue in colorblind mode) in the interface when things are fine, but if a suspicious event occurs, it will turn red, notifying the user of an incident. After which, a user can then connect to the device's Wi-Fi access point and log in to the web interface to learn more about the event.
One of the primary objectives of Rayhunter to collect data on how often CSS is used to monitor free expression, particularly during events like protests and religious gatherings. The EFF hopes that this will help them understand how these tools are deployed so that they can raise awareness of their impact on privacy and assist the cellular security research community in building better defenses against CSS.
Do you want one?
After you procure the Orbic device (linked above), setting up Rayhunter is quite straightforward. You just have to download the latest release from the project's GitHub repo, unzip the package, and plug the Orbic device into your Linux or macOS device.
After that, run one of the following scripts to get it installed:
install-linux.sh # For Linux (tested on recent versions of Ubuntu)
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