Huh, that is interesting. Though, that post doesn't seem to have any info about what the backdoor is either.

Tarlogic Security has detected a backdoor in the ESP32, a microcontroller that enables WiFi and Bluetooth connection and is present in millions of mass-market IoT devices. [...] This discovery is part of the ongoing research carried out by the Innovation Department of Tarlogic on the Bluetooth standard. Thus, the company has also presented at RootedCON, the world’s largest Spanish-language cybersecurity conference, BluetoothUSB, a free tool that enables the development of tests for Bluetooth security audits regardless of the operating system of the devices. [Emphasis mine.]

Maybe the presentation has nothing to do with the actual backdoor?

Though, this part later might seem to imply they are related:

In the course of the investigation, a backdoor was discovered in the ESP32 chip, [...] Tarlogic has detected that ESP32 chips [...] have hidden commands not documented by the manufacturer. These commands would allow modifying the chips arbitrarily to unlock additional functionalities, [...].

Which, best I can work out, seems to be talking about the information on slide titled "COMANDOS OCULTOS" (page 39 / "41").

If the "backdoor" is the couple of commands in red on that slide, I maintain what I said above. If it's not talking about that and there's another "backdoor" that they haven't described yet, well, then ¯\_(ツ)_/¯ we'll see what it is when they actually announce it.

I fully acknowledge there may be something I'm missing. If there's a real vuln/backdoor here, I'm sure we'll hear more about it.