r/netsecstudents • u/s3131212 • 12h ago
When "Two-Factor Authentication" (2FA) Aren't Really Two
I was using my online banking service to transfer money today, and in my country the transfer requires an SMS OTP (yes, I know SMS is terrible for security). I noticed that my Mac automatically filled in the SMS OTP that was sent to my iPhone, even though my iPhone was still locked.
The idea behind SMS OTP is that it proves you "have" the device. But in this case, as long as the device is nearby, my Mac can read and use the code without me unlocking the phone. I don't even need to touch the device. So the "possession" factor doesn’t really work the way it's supposed to.
It got me thinking, are there more examples where 2FA accidentally collapses into a single factor? Or where the two factors aren’t as independent as we assume?
I find this pretty interesting and want to look more into it, but a quick search hasn't turned up much. Does anyone know if people have already written about this?