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Undocumented Commands Found In Bluetooth Chip Manufactured in China Used By a Billion Devices.
(www.tarlogic.com)
This is a most excellent place for technology news and articles.
This is about silicon. Undocumented instructions have just been found in it but they are not executable unless the ESP32's firmware uses them. Firmware cannot be edited to use them unless you have an existing vulnerability such as physical access or insecure OTA in existing firmware (as far as researchers know).