Hidden Commands in ESP32: Security Implications for Your Smart Devices

Security researchers have recently uncovered a significant finding in one of the most widely-used microcontrollers in the IoT world—and it’s something everyone with smart devices should be aware of.

Spanish researchers from Tarlogic Security presented their findings at RootedCON, revealing that the ESP32 chip—used in billions of devices from smart plugs and lights to security cameras and even medical equipment—contains undocumented commands that, under certain conditions, could potentially introduce security risks.

Update (March 15, 2025): This article has been updated to reflect clarifications from both the researchers and Espressif (the chip manufacturer). The original research initially characterized these hidden commands as a “backdoor,” but this terminology was later corrected. The manufacturer has also provided technical context and is releasing mitigation measures despite assessing the actual risk as low for most deployments.

What’s Actually Happening Here?

Let me break down what this means in plain language:

Researchers found that the ESP32 chip contains 29 undocumented Host Controller Interface (HCI) commands in the Bluetooth firmware. These commands weren’t mentioned in any official documentation but allow operations like:

  • Reading and writing to RAM memory
  • Reading flash memory
  • Modifying Bluetooth functionality
  • Potentially altering device behavior

Espressif, the chip’s manufacturer, has explained that these are debug commands included for testing purposes during development—a common practice in embedded systems—and not a deliberate backdoor.

Important Context and Limitations

Before panicking, here are some critical facts about this discovery:

  1. Physical or local access is typically required: To exploit these commands, an attacker would generally need physical access to the device’s hardware or to be within Bluetooth range.

  2. Most common ESP32 configurations aren’t vulnerable: In the most common use case where the Bluetooth host and controller both run on the ESP32 itself, the application already has full privileged access to memory and registers, so these commands don’t introduce additional risk.

  3. Limited scope: Only the original ESP32 chip is affected, not the newer ESP32-C, ESP32-S, and ESP32-H series.

  4. CVE assigned: This issue has been assigned CVE-2025-27840.

The primary risk is in less common configurations where the ESP32 acts as a Bluetooth coprocessor for another system via serial interfaces. In such configurations, if the host system is compromised, an attacker could potentially use these commands to influence the ESP32’s behavior.

It’s In Everything

The real concern is how ubiquitous this chip is. The ESP32 has become the de facto microcontroller for affordable IoT devices due to its low cost (around $2) and solid performance. It’s found in:

  • Those inexpensive smart plugs from Amazon
  • Budget smart light systems
  • Temperature sensors
  • Security cameras
  • Smart locks
  • Baby monitors
  • Some medical devices

Espressif reported in 2023 that over a billion ESP32 units had been sold worldwide.

Espressif’s Response

To their credit, Espressif has been transparent in their response. They’ve published a detailed technical explanation clarifying:

  1. These commands cannot be triggered remotely over Bluetooth or the Internet unless there’s already a vulnerability in the application or radio protocols
  2. For most applications, there’s minimal to no security risk
  3. They’re still providing a software fix to remove access to these debug commands
  4. They’ll document all vendor-specific HCI commands going forward for transparency

According to Espressif: “While these debug commands exist, they cannot, by themselves, pose a security risk to ESP32 chips. Espressif will still provide a software fix to remove these undocumented commands.”

The company has committed to releasing a software patch for currently supported ESP-IDF versions to remove access to these debug commands and has assigned the identifier CVE-2025-27840 to the issue.

What Should You Do?

While the actual risk for most consumer devices is lower than initially reported, there are still some reasonable precautions to take:

  1. Keep your devices updated: Apply firmware updates when available, as manufacturers may incorporate Espressif’s fixes.

  2. Network segmentation is still good practice: Consider placing IoT devices on a separate network from your main devices, limiting what they can access.

  3. Be cautious with high-security applications: If you’re developing products using ESP32 for security-critical applications, consider:

    • Using the newer ESP32 chip series that don’t have these commands
    • Applying Espressif’s patches when available
    • Implementing additional security measures

  4. Physical security matters: Remember that many IoT vulnerabilities require physical access, so secure placement of critical devices remains important.

To see the technical details of the research and Espressif’s response, you can check out:

The Bigger Picture

This discovery highlights a broader issue in IoT security: the challenge of balancing development convenience with security rigor. Debug features left enabled in production hardware is a common finding across the industry.

The difference between alarming security headlines and actual risk often comes down to context. In this case, what was initially described as a “backdoor” turned out to be undocumented debug commands—still a security concern worth addressing, but with important limitations that significantly reduce the practical risk for most users.

This doesn’t diminish the importance of security research like Tarlogic’s work. It’s precisely this kind of discovery that pushes manufacturers to improve transparency and security practices, benefiting the entire ecosystem.

For now, I’m giving my smart devices a more critical look, but not throwing them out. Understanding the actual risks rather than just the headlines helps make informed decisions about the technology we invite into our homes.

What smart devices do you have that might be using this chip? Are you concerned? Drop your thoughts in the comments – I’m especially interested in hearing from security folks who’ve been tracking this.