
Once the handset is connected the base station pushes firmware to its baseband processor, a chip that handles voice calls, and that firmware routes the calls through the malicious base station from where they are directed to a proxy that records calls and sends them to the attacker. All of this happens without the user ever knowing about it, they can continue to make and receive calls while they're recorded in the background as if the line had a wiretap on it. The researchers have not made the full details of this attack public for obvious reasons but they have disclosed it to Samsung which will hopefully have a fix ready in the near future.