CellGuard is a research project that analyzes how cellular networks are operated and possibly surveilled.

CellGuard is a research initiative from the Secure Mobile Networking Lab at the Technical University of Darmstadt, focusing on analyzing cellular network operations and detecting potential surveillance activities. Central to this project is the CellGuard iOS app, designed to identify and alert users to rogue base stations—malicious network cells that deceive phones into connecting, enabling attackers to track locations, intercept communications, or exploit device vulnerabilities.

 

cellguard.seemoo.tu-darmstadt.de

 

 

 

How CellGuard Detects Rogue Base Stations:

 

The app monitors baseband packets on iPhones, analyzing them for suspicious patterns indicative of rogue base stations. Detection metrics include:

 

• Location Database Cross-References: Comparing detected base stations with Apple's Location Services (ALS) database to identify cells that are newly established or have incorrect parameters.
• Signal Analysis: Assessing signal strength anomalies, as rogue stations often emit stronger signals to force connections.
• Bandwidth Checks: Identifying base stations using outdated or low-cost hardware, which are often associated with rogue installations.
• Network Reject Packets: Detecting failed network authentication attempts, which may indicate malicious activity.
• While these metrics enhance detection capabilities, legitimate network changes—such as newly deployed base stations or network congestion—can trigger false positives.

 

cellguard.seemoo.tu-darmstadt.de

 

 

 

Technical Insights and Public Participation:

CellGuard captures packets exchanged between the iPhone’s baseband chip and iOS, processing them in real-time to detect irregularities. Users can contribute to the project's development by testing the app, providing feedback, reporting issues, or submitting new features and bug fixes.

 

Open-Source and Privacy-First Approach:

CellGuard is open-source, with its code available on GitHub under the GPL-3.0 license, encouraging community participation in enhancing the app's functionality. The project prioritizes privacy, adhering to principles of minimal data usage and offline-first data processing. All personal data is stored locally on the device, and only anonymized information is shared with the research team if users opt into the study. No data is sold or shared with third parties.