Physical UART Access Leading to an Unauthenticated Root Shell in TP-Link Kasa EC70 and EC71

Kasa EC70 v4 and EC71 v4 do not logically disable the production debug interface at the firmware or chip level and do not lock the bootloader.  Although the debug traces are physically severed during manufacturing, an attacker with physical access can restore the connection, interrupt the boot process, and manipulate boot parameters to enter a non-standard initialization path that exposes an unauthenticated root shell during startup. Successful exploitation may allow an attacker with physical access to obtain root-level command access during device startup, resulting in loss of confidentiality, integrity, and availability for the affected device. Exploitation requires device disassembly, restoration of the severed debug connection, and manipulation of the boot process.