It’s ofono that manages this.
My tool uses the QML interface to ofono, but you can access it with dbus:
$ busctl introspect org.ofono /ril_0 org.ofono.CellBroadcast
NAME TYPE SIGNATURE RESULT/VALUE FLAGS
.GetProperties method - a{sv} -
.SetProperty method sv - -
.EmergencyBroadcast signal sa{sv} - -
.IncomingBroadcast signal sq - -
.PropertyChanged signal sv - -
See here: Is there any way to disable cell broadcast messages? - #12 by adekker