Today I analyzed my home router.
I connected a keyboard to the router's USB port, which is usually used for mass storage devices. However, I pressed the key combination to reboot a Linux system from TTY (<Ctrl>-<Alt>-<Del>) multiple times. Afterwards the router actually rebooted.
Now, for me this is a strong indication I can blindly access a TTY with the keyboard. If I knew a username and a password I'd most likely be able to login.
To prevent this, the router manufacturer could disallow USB Keyboards.
But else what could they do to prevent this behaviour? Is it sufficiant to disable all TTYs? Can I build a Linux without a login possibility?