Gr-GSM — GNU Radio GSM Receiver & Decoder

Gr-GSM is a set of GNU Radio out-of-tree (OOT) blocks implementing a GSM receiver for passive over-the-air capture. Within TelcoChisel, Gr-GSM is pre-installed with live monitoring tools, Wireshark GSMTAP integration, and support for RTL-SDR, HackRF, and USRP hardware for real-time GSM signal analysis and IMSI catcher detection.

Key Capabilities & Security Vectors

• Passive GSM Capture: Receive and decode GSM downlink channels (BCCH, SDCCH, TCH) without active transmission.
• GSMTAP Wireshark Integration: Stream decoded GSM frames in real-time to Wireshark for LAPDm, RR, MM, and CC protocol analysis.
• Cell Information Extraction: Decode System Information messages to extract MCC, MNC, LAC, Cell ID, and neighboring cell lists.
• IMSI Catcher Detection: Monitor paging channels for plaintext IMSI transmissions indicating active IMSI catchers.

TelcoChisel Execution Cheatsheet

1. Live GSM Monitoring with GUI

# Launch interactive GSM monitor with frequency selector
grgsm_livemon -f 935.2e6

2. Headless Capture to Wireshark

# Capture BCCH and pipe to Wireshark via GSMTAP
grgsm_livemon_headless -f 935.2e6 | wireshark -k -i lo -f "udp port 4729"

3. Scan for Active GSM Channels

# Scan and list all active GSM ARFCN channels in range
grgsm_scanner --band GSM900 --speed 2

Practice in TelcoSec Academy

👉 Launch GSM Sniffing Lab on App.TelcoSec.Net