: Some secret firmware allows a GSM module to act as a fake BTS (cell tower) for MITM attacks, without requiring full OpenBTS or YateBTS setups.
The secrecy surrounding this firmware has historically led to a "security by obscurity" approach, which researchers argue makes devices more vulnerable. gsm+secret+firmware
This is the most famous open-source project for GSM mobile stations. It allows you to replace the proprietary baseband firmware on specific older phones (like the Motorola C115/C118) with open-source code to see how GSM actually works. You can find their documentation at Osmocom.org . : Some secret firmware allows a GSM module
Governments could mandate that baseband firmware be auditable or that source code escrows be maintained for security evaluation, moving away from the "black box" model currently prevalent in the industry. It allows you to replace the proprietary baseband