Chinese-Made Zbtlink Routers Ship With Backdoor That Opens Unauthenticated Root Shells

Zbtlink routers shipped with a deliberate, factory-installed backdoor (ENDLESSDOORS) that provides unauthenticated root shell access and communicates with Chinese command-and-control infrastructure — meaning compromise begins the moment a device is powered on. This is a classic supply chain attack embedded at the firmware level, bypassing any post-deployment security controls entirely. The backdoor persisted across over two years of firmware images, indicating either intentional inclusion or a catastrophic failure in the vendor's secure development lifecycle. Organizations deploying these devices unknowingly handed adversaries persistent, privileged access to their networks with no user interaction required. This underscores why hardware and firmware provenance must be validated before any device is introduced into a production environment.