I got a unit with disabled telnet and UART. But it was possible for me to start the TFTP recovery process and interrupt it after loading the image when it starts erasing the flash by just pulling the power cord.
After power on it is not able to load anything and falls back into UBoot with a working UART terminal that can be used not only for enabling telnet and SSH, but also for loading an OpenWRT image and starting it.
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