Ye Lin's Random stuff

My random notes

07 Nov 2021

Things I Read - SIM Cards!

Another rainy day.

SIM Cards!!

Another day, another interesting HN post. I saw this post What is AT&T doing at 1111340002?.

And the top was very interesting to me.

Even in relatively technical circles, like HN, many people are not aware of this and I use every opportunity I have to reiterate:

A SIM card is a full-blown computer with its own CPU and memory.

Your carrier can upload and run arbitrary code without your consent or knowledge. They can do this at any time. This means that your “phone” is actually three different computers running in concert - the actual phone itself (iOS or Android or Symbian), the baseband processor running the baseband code, and the SIM card.


I did not know that!

Another thing is I have noticed in the past is whenever I insert my SIM card, there would be some application appearing automatically. The most likely explanation could be this

This was driven home to me many years ago when I popped a SIM from a Mexican carrier that had an embedded Dominos Pizza app on it. Suddenly the Windows Mobile phone I was testing had a new icon on it.

Likely the app was not embedded in the sim. It was likely a carrier profile that the sim activated that triggered the download and install of the app.


And this DefCon talk from 2013 was awesome!

Defcon 21 - The Secret Life of SIM Cards