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[Ed note: Most of the headlines for this story uses the security vendor's description of this is a "backdoor", which is getting called out as deliberate clickbait and hype given the physical access needed to load malicious code --hubie]
Undocumented commands found in Bluetooth chip used by a billion devices
The ubiquitous ESP32 microchip made by Chinese manufacturer Espressif and used by over 1 billion units as of 2023 contains an undocumented "backdoor" that could be leveraged for attacks.
The undocumented commands allow spoofing of trusted devices, unauthorized data access, pivoting to other devices on the network, and potentially establishing long-term persistence.
This was discovered by Spanish researchers Miguel Tarascó Acuña and Antonio Vázquez Blanco of Tarlogic Security, who presented their findings yesterday at RootedCON in Madrid.
"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," reads a Tarlogic announcement shared with BleepingComputer.
"Exploitation of this backdoor would allow hostile actors to conduct impersonation attacks and permanently infect sensitive devices such as mobile phones, computers, smart locks or medical equipment by bypassing code audit controls."
The researchers warned that ESP32 is one of the world's most widely used chips for Wi-Fi + Bluetooth connectivity in IoT (Internet of Things) devices, so the risk of any backdoor in them is significant.
In their RootedCON presentation, the Tarlogic researchers explained that interest in Bluetooth security research has waned but not because the protocol or its implementation has become more secure.
Instead, most attacks presented last year didn't have working tools, didn't work with generic hardware, and used outdated/unmaintained tools largely incompatible with modern systems.
Tarlogic developed a new C-based USB Bluetooth driver that is hardware-independent and cross-platform, allowing direct access to the hardware without relying on OS-specific APIs.
Armed with this new tool, which enables raw access to Bluetooth traffic, Targolic discovered hidden vendor-specific commands (Opcode 0x3F) in the ESP32 Bluetooth firmware that allow low-level control over Bluetooth functions.
In total, they found 29 undocumented commands, collectively characterized as a "backdoor," that could be used for memory manipulation (read/write RAM and Flash), MAC address spoofing (device impersonation), and LMP/LLCP packet injection.
Espressif has not publicly documented these commands, so either they weren't meant to be accessible, or they were left in by mistake.
The risks arising from these commands include malicious implementations on the OEM level and supply chain attacks.
Depending on how Bluetooth stacks handle HCI commands on the device, remote exploitation of the backdoor might be possible via malicious firmware or rogue Bluetooth connections.
This is especially the case if an attacker already has root access, planted malware, or pushed a malicious update on the device that opens up low-level access.
In general, though, physical access to the device's USB or UART interface would be far riskier and a more realistic attack scenario.
"In a context where you can compromise an IOT device with as ESP32 you will be able to hide an APT inside the ESP memory and perform Bluetooth (or Wi-Fi) attacks against other devices, while controlling the device over Wi-Fi/Bluetooth," explained the researchers to BleepingComputer.
"Our findings would allow to fully take control over the ESP32 chips and to gain persistence in the chip via commands that allow for RAM and Flash modification."
"Also, with persistence in the chip, it may be possible to spread to other devices because the ESP32 allows for the execution of advanced Bluetooth attacks."
BleepingComputer has contacted Espressif for a statement on the researchers' findings, but a comment wasn't immediately available.
= https://www.documentcloud.org/documents/25554812-2025-rootedcon-bluetoothtools/
= https://reg.rootedcon.com/cfp/schedule/talk/5
= https://www.tarlogic.com/news/backdoor-esp32-chip-infect-ot-devices/
(Score: 2) by VLM on Tuesday March 11, @01:35PM
Aside from the "Security backdoor" yelling, this should be helpful for reverse engineering, which depending upon your relationship to the device is either really good or really bad. If you already have physical access to the device and can put it in what is essentially debug mode, this seems to make a lot of things easier but doesn't seem to enable anything entirely new.
My guess is there's a lot of generated noise about "security backdoor" that does not technically exist, to keep the more interesting and accurate story about it being much easier than previously believed to reverse engineer, quiet. Let's all talk about security holes that don't exist and clickbait and similar noisy topics, while not discussing the interesting topic of how its apparently going to be a lot easier to reverse-engineer stuff in the future. Is this intentional/funded or merely coincidence? Hard to say.
The only pure net positive is I think you could write an ESP32-specific debugger that leverages those interesting features to do some cool unique and interesting debugging stuff. Who knows maybe someday in the Arduino IDE (which supports espressif chips) you'll be able to change MAC addresses on the fly on running code via a dropdown menu or some of those other odd, interesting features.