Lock the memory so that update is physical only and restart regularly to avoid no-memory malware. Not 100% secure and very inconvenient, so people prefer to isolate IOT in its own network and preferably have a good network security like putting the devices behind VPN/firewall/other gatekeeper.
Actually, if you want to have IOT access outside of the network, the best approach is to close all ports and for the device to initiate connection with a control server. The device is dark when scanned while a heartbeat signal will ensure connectivity. This will require a good security on the control server, but that is okay because server security is much better understood and does not suffer from the constraints of the embedded software.
Actually, if you want to have IOT access outside of the network, the best approach is to close all ports and for the device to initiate connection with a control server. The device is dark when scanned while a heartbeat signal will ensure connectivity. This will require a good security on the control server, but that is okay because server security is much better understood and does not suffer from the constraints of the embedded software.