Hidden Bluetooth Commands in ESP32 Chips: Should We Be Worried?

Last week, I went down a rabbit hole after reading about some Spanish security researchers who found a bunch of hidden Bluetooth commands in those ubiquitous ESP32 microchips. You know the ones – they're in practically every smart gadget these days (over a billion shipped worldwide!). Since a few colleagues have asked me about it, I figured I'd share what I've learned and my take on whether this is actually something to lose sleep over.

What's the deal?

So here's what happened: researchers from Tarlogic Security found 29 undocumented Bluetooth commands buried in ESP32's firmware. These aren't your standard commands – they let you:

• Read and write directly to the chip's memory (yikes)
• Change the device's Bluetooth MAC address (hello, identity theft)
• Mess with low-level Bluetooth packets

They presented this at RootedCON a couple weeks ago, and it's now officially tracked as CVE-2025-27840.

Should we panic?

After digging into this, I'm filing it under "concerning but not catastrophic." Here's why:

First, these aren't remote exploits – you can't just walk around zapping ESP32 devices with your phone. An attacker would need to already have compromised your device through some other vulnerability or have physical access to it.

Essentially, these commands are more useful to an attacker after they've already broken in. Think of it like finding a hidden passage in a house after you've already picked the front door lock.

The real concern is what a determined attacker could do once they've found that passage:

• Plant malware that survives reboots and firmware updates
• Make your device impersonate other trusted Bluetooth gadgets
• Use your compromised device to attack other nearby Bluetooth devices

How's Espressif handling it?

Credit where it's due – Espressif hasn't gone into corporate denial mode. They've:

• Acknowledged these were debugging features left in (oops)
• Clarified that newer chip variants (ESP32-C3, S3, and H series) don't have these issues
• Promised firmware updates to remove or disable these commands

What I'm doing about it

For my own projects using ESP32:

1. I'm keeping an eye out for Espressif's patches and will update firmware ASAP
2. For the personal projects where I'm using ESP32 in "standalone mode" (which is most of them), I'm not too worried
3. For the few where I'm using an external processor to talk to the ESP32, I'm double-checking that my HCI interfaces aren't easily accessible

The bigger picture

What bugs me most isn't this specific issue – it's what it represents. We're building our connected world on components with features even their makers don't fully document. That's... not great.

This whole situation reminds me of that time back in 2015 when I spent weeks debugging weird network behavior only to discover an undocumented "feature" in a router chip. Lesson learned: hardware transparency matters just as much as software transparency.

Your thoughts?

Has anyone else been working with ESP32 chips? Are you planning any changes to your development process after this news? Would love to hear your experiences or concerns in the comments.

Coffee-fueled thoughts based on security research presented at RootedCON in March 2025. I've tried to be accurate, but this isn't my day job, so defer to Espressif's official word on anything critical.