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Why would an Internet radio appliance need to broadcast an SSID? (infosec.pub)

submitted 1 month ago by daveyOsborn@infosec.pub to c/homenetworking@selfhosted.forum

6 comments fedilink hide all child comments

A DAB/Internet radio (made by Karcher in Germany) broadcasts an SSID (details). It cannot be disabled and neither the SSID nor the MAC address can be changed.

Can someone explain why this is necessary?

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[–] daveyOsborn@infosec.pub 2 points 1 month ago* (last edited 1 month ago) (1 children)

So IIUC, you’re saying it’s for a phone to configure the appliance? The reason being that the appliance’s UI is not convenient enough, I presume?

In the case at hand, the Karcher DAB radio has no iOS or AOS app. So AFAICT it would only be feasible if the radio also had a built-in web server and a captive portal. But I get no captive portal when connecting.

I suppose another theory is that if the radio has a cloud uplink, perhaps it would then push a captive portal to redirect to a centralised server which then remotely configures the device. I would not trust it enough to give it an uplink so I can’t test this theory.

[–] ChaoticNeutralCzech@feddit.org 2 points 1 month ago* (last edited 1 month ago)

It doesn't need an app to set up over Wi-Fi, that's one advantage of this technique. It works like this:

Device acts as access point: either open, WPS or showing the password/QR code on screen
Connect phone (or computer etc. with browser) to the access point
The phone will try to connect to a known domain (for example http://connectivitycheck.gstatic.com/ on stock Android) to determine if the AP has Internet access. If this doesn't work, go to an HTTP-only site: http://neverssl.com/
The device will hijack the unencrypted HTTP request and redirect to http://192.168.1.1/setup.html or whatever (this will be detected by the phone as "captive portal" and you get a "Sign in to Wi-Fi network" notification (the phone believes it may then access the internet because some Wi-Fi hotspots do this)
You input your home network's credentials into the webpage so you don't have to dial them in with the volume knob and tiny buttons
The device disables its setup hotspot (if only one Wi-Fi radio is available) and tries to connect to the provided network (usually there's a timeout so the process restarts on failure)

This is very common, I made an ESP32 device whose setup works like this. If you need to make an open Wi-Fi network for whatever reason, you can name it "HP Deskjet Pro 4800" and it's very unlikely someone searching for public Wi-Fi will try to connect