The [ESP32 Vulnerability] making headlines isn’t your average glitch. This chip, developed by Chinese manufacturer Espressif, powers more than a billion devices. Researchers now warn that it includes mysterious, undocumented commands that attackers could weaponize to spoof devices, steal data, and even pivot into broader network infiltration.
Keep reading to learn how two Spanish security experts found these hidden functions, why the risk is massive for IoT devices, and how attackers might exploit this brand-new backdoor.
Background on the ESP32 Chip
The ESP32 has become a go-to microcontroller for engineers and hobbyists worldwide. It supports Wi-Fi and Bluetooth connectivity, making it an ideal pick for devices ranging from fitness trackers to smart locks. Its efficiency, low cost, and reliable design led to swift adoption by businesses seeking to embed wireless networking into their products.
However, behind its success lies the newly discovered [ESP32 Vulnerability]. Researchers say it involves a set of overlooked commands tucked away in the chip’s firmware. These commands go well beyond official documentation, raising questions about why they exist and how they remained unknown for so long.
Discovery by Tarlogic Security
Spanish security experts, Miguel Tarascó Acuña and Antonio Vázquez Blanco, from Tarlogic Security, delivered a jaw-dropping presentation at RootedCON in Madrid. They revealed that hidden instructions within the ESP32 firmware could let hostile actors bypass crucial security controls. In an official statement shared with BleepingComputer, Tarlogic emphasized the seriousness of this issue:
“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.”
According to Tarlogic, these hidden instructions—unmentioned by Espressif—are akin to a secret doorway. Attackers can sneak in and manipulate everything from memory contents to Bluetooth addresses. Once inside, cybercriminals can mount a variety of attacks, potentially leaving little trace behind.
Why the [ESP32 Vulnerability] Matters
The scale of this discovery cannot be overstated. Because the ESP32 chip appears in countless devices, any weakness at its core might compromise entire networks. Hackers can spoof trusted hardware, making it appear legitimate. They can also read or write directly to system memory, injecting their own code or siphoning out sensitive data.
Even more concerning is the potential for lateral movement. Once an attacker hijacks an ESP32-equipped device, they can pivot to other connected systems, especially if weak passwords or unpatched software provide easy entry points. This technique lets threat actors escalate their access and potentially compromise central systems, such as company servers or high-value personal devices.
How Undocumented Commands Were Found
Declining Interest in Bluetooth Attacks
Tarlogic researchers pointed out a puzzling drop in Bluetooth security research over recent years. They argue that this lull doesn’t necessarily signal improved Bluetooth safety. Instead, researchers might have lost interest due to outdated tools or specialized hardware requirements.
Creating a Fresh Toolset
To tackle these challenges, Tarlogic built a new C-based USB Bluetooth driver. It’s hardware-independent and cross-platform, offering raw access to Bluetooth traffic regardless of the operating system. By bypassing OS-level APIs, researchers could inspect low-level data transmissions.
This approach led them to discover a set of vendor-specific commands tied to opcode 0x3F in the ESP32 Bluetooth firmware. These are commands that Espressif didn’t publicly document. As a result, the potential for misuse took the security community by surprise.
Details of the Hidden Commands
The Tarlogic team uncovered 29 undocumented commands that together create a dangerous “backdoor.” This backdoor can:
- Read/Write Memory (RAM and Flash): Attackers can alter firmware or operating instructions.
- Spoof MAC Addresses: By faking a device’s Bluetooth identity, hackers can impersonate legitimate devices.
- Inject LMP/LLCP Packets: These low-level Bluetooth traffic packets are key in how devices communicate. Gaining control means attackers could manipulate core Bluetooth processes.
Espressif hasn’t published an official explanation for these hidden instructions. Whether they were intentionally introduced for debugging or accidentally left in production remains unclear. The vulnerability is now tracked as CVE-2025-27840, though it’s unknown when or how the vendor plans to address it.
Real-World Threats: From Supply Chain Attacks to Malware
Supply Chain Concerns
Supply chain attacks exploit the fact that many devices share the same foundational components or software. If an OEM (Original Equipment Manufacturer) uses compromised ESP32 chips, the infiltration can spread throughout their product line. This type of backdoor is difficult to detect in routine audits, especially when the commands are undocumented.
Remote Exploitation
While physical access via USB or UART dramatically simplifies exploitation, Tarlogic warns remote abuse could be possible. If hackers already control a device’s firmware or can push malicious updates, they might activate the ESP32 backdoor from afar. This scenario is especially alarming for widely-deployed IoT gadgets, where a single exploit can scale up to thousands—if not millions—of devices.
Persistence and Network Movement
Once inside the system, attackers might inject persistent malware that remains active even after reboots or partial software patches. They can then launch advanced Bluetooth-based assaults on nearby devices, turning one compromised ESP32 into a stepping stone for broader attacks. This method may be particularly devastating in networks where multiple IoT devices work together, from industrial control systems to home automation.
How Attackers Might Exploit This Vulnerability
- Gaining Initial Access: Attackers could trick users into installing malicious firmware updates or plant malware through USB debugging interfaces.
- Deploying the Undocumented Commands: Using these secret instructions, they gain direct control over the chip’s memory, network addresses, and Bluetooth stack.
- Establishing Persistence: By injecting malicious code into the memory, hackers can ensure the device remains compromised long-term, evading conventional security checks.
- Spreading Laterally: Equipped with the ability to spoof Bluetooth addresses or manipulate Wi-Fi, attackers can quietly scout for more targets, forging a path through the network.
- Maintaining Stealth: Because these commands are not officially documented, traditional endpoint security solutions might miss the malicious activity.
Industry Response and Next Steps
The Tarlogic researchers shared their findings with Espressif, but there has been no immediate public statement. Experts expect the vendor to release a patch or official explanation soon, given the severity of the situation. Meanwhile, security professionals advise anyone deploying ESP32-based systems to conduct urgent reviews of current firmware and network configurations.
Mitigation Tips
- Patch and Update: Watch for official vendor patches and apply them swiftly.
- Monitor for Suspicious Activities: Keep an eye on unusual Bluetooth behavior or unknown MAC addresses in your environment.
- Lock Down Debug Ports: If possible, disable or password-protect UART interfaces and other open ports commonly used for debugging.
- Use Network Segmentation: Segment IoT devices on isolated networks. This step limits lateral movement if one device is breached.
- Adopt Zero Trust Principles: Verify every connection, even if it appears to come from a trusted internal device.
A Wake-Up Call for IoT Security
The [ESP32 Vulnerability] is a grim reminder that hidden weaknesses can lurk in the most trusted hardware. With billions of these chips deployed globally, a single misstep in patching or network segmentation can lead to breaches on an unprecedented scale. Security researchers at Tarlogic have sounded the alarm. Now, it’s up to the entire IoT ecosystem—developers, manufacturers, and consumers—to heed these warnings and safeguard our connected world. Keep an eye on Startupmars for more news on security.
