Summary
In October, Microsoft published an analysis which found that a Chinese hacking entity had access to a trove of compromised TP-Link routers.
The Justice Department is also investigating whether TP-Link’s low pricing violates U.S. antitrust laws.
TP-Link denies selling below cost and claims its security practices meet U.S. standards.
The potential ban highlights growing scrutiny of Chinese tech products used widely in homes, businesses, and even U.S. federal agencies.
And to complement your answer, the place where a custom firmware might still be compromised is mostly in the binary blobs, where proprietary code for the radios and some other chips aren’t open-source and act like some kind of black box between the software and the hardware and make it work.
Unless someone reverse-engineer those blobs and make an open-source alternative.
Hardware backdoors are also possible in the silicon, and are probably some of the most dangerous. Fortunately also probably some of the most sophisticated and difficult to introduce.