Full Report
The ubiquitous ESP32 microchip made by Chinese manufacturer Espressif and used by over 1 billion units as of 2023 contains undocumented commands that could be leveraged for attacks. [...]
Analysis Summary
# Vulnerability: Undocumented Backdoor Commands in ESP32 Bluetooth Firmware
## CVE Details
- CVE ID: CVE-2025-27840
- CVSS Score: Information Not Available (Severity Not Explicitly Stated)
- CWE: Insufficient Control of System Interface (Potential)
## Affected Systems
- Products: Devices utilizing ESP32 chips with Bluetooth functionality.
- Versions: ESP32 Bluetooth firmware where the undocumented vendor-specific commands (Opcode 0x3F) are present. (Specific versions not detailed in the summary).
- Configurations: Devices where an attacker has low-level access (e.g., root access, via physical USB/UART, or through supply chain compromise).
## Vulnerability Description
Researchers discovered 29 undocumented vendor-specific commands (Opcode 0x3F) within the Bluetooth firmware of ESP32 chips. These commands effectively act as a "backdoor," allowing low-level control over the hardware's Bluetooth functions. The commands enable critical operations such as memory manipulation (reading/writing RAM and Flash), MAC address spoofing (device impersonation), and injection of LMP/LLCP Bluetooth packets. These commands were likely left in by mistake or were not intended for public access.
## Exploitation
- Status: PoC available (Implied by the research demonstrating functionality, though "in the wild" status is not mentioned).
- Complexity: Low to Medium (Requires low-level access, physical access is considered a more realistic scenario than purely remote exploitation without prior compromise).
- Attack Vector: Primarily Local/Physical (via USB or UART interface) or via established system compromise (Root access/malware planting) leading to low-level stack access. Potential for remote exploitation exists if Bluetooth stacks inadequately guard against HCI command handling.
## Impact
- Confidentiality: High (Ability to potentially read Flash/RAM contents).
- Integrity: High (Ability to modify Flash/RAM, leading to persistence and system corruption).
- Availability: High (Ability to disrupt Bluetooth functions or maintain persistence).
## Remediation
### Patches
- Remediation status is pending specific vendor confirmation, but users should seek official firmware updates from Espressif or device manufacturers addressing CVE-2025-27840.
### Workarounds
- Restrict physical access to devices containing ESP32 chips.
- Ensure that input handling for HCI commands originating from non-trusted sources is strictly validated, especially if direct hardware access is possible (e.g., avoiding direct forwarding of commands if only OS APIs should be used normally).
- Thoroughly vet firmware updates in the supply chain layer.
## Detection
- Indicators of Compromise: Unexpected device persistence, unauthorized device impersonation (MAC spoofing), or unusual write operations to Flash/RAM via Bluetooth interfaces.
- Detection methods and tools: Deep inspection of Bluetooth HCI commands, potentially requiring specialized tools (like the C-based driver used by the researchers) to observe traffic hitting the hardware layer directly, bypassing standard OS APIs.
## References
- Vendor advisories: Pending explicit advisory from Espressif regarding CVE-2025-27840.
- Relevant links:
- bleepingcomputer com/news/security/undocumented-commands-found-in-bluetooth-chip-used-by-a-billion-devices/