Without proper means of prevention, the weak link lies in your own network and the public internet. Tools such as wireshark can trivially capture your network traffic and re-assemble the packets to readable call metadata and audio files.
Securing your own network
The closer the attacker is to your phone, the smaller the net he needs to cast. This makes your own network the most likely starting point for any attacker. The attacker could use tools like wireshark to capture all network traffic, or simply use the build-in web interface of your phone to enable a capture.
Below you will find some tips to get you started:
• Change the default usernames and passwords of your phone;
• Separate your phone from the rest of your network by using separate VLANs or a separate physical network;
• Only allow known devices access to your phone network, for instance by using a MAC Address Filter;
• Deny access to your phone network from your other networks (eg computers, wifi);
• Configure your firewall to only allow external access to your phone from the Kwebbl network;
• Enable the IP whitelist on Kwebbl for every device to only allow access to the SIP account from the configured IP address.