ESP32: hidden HCI commands allowing unauthorized access (CVE-2025-27840) #shorts

Summary

Welcome to today's podcast where we delve into the details of a recent security vulnerability affecting Espressif ESP32 chips, identified as CVE-2025-27840. Discovered earlier this year, this vulnerability involves unexpected hidden functionalities within the chip that could potentially be exploited for privilege escalation.

Product details

Espressif's ESP32 is a popular chip used for IoT applications, known for its versatility in wireless communication and low power consumption. However, recent investigations have uncovered security vulnerabilities that require immediate attention from users and developers.

Vulnerability type summary

The vulnerability in question is classified under CWE-912, which involves hidden functionalities within the system. In the case of the ESP32, these are 29 HCI commands that are not inherently visible or known to the typical user, opening doors to potential exploitation.

Details of the vulnerability

CVE-2025-27840 describes a situation where Espressif ESP32 chips allow hidden HCI commands, such as the command 0xFC02, which can write to memory and perform unauthorized actions. While there's no confirmed presence of a backdoor, the vulnerability could lead to privilege escalation if exploited, thereby providing unauthorized access to the device.

Conclusion

In conclusion, while Espressif has clarified that there's no programmed backdoor, the hidden commands in the ESP32 pose significant security risks. Users and developers should stay informed and update their systems as patches become available. It's crucial to mitigate any threats by ensuring robust security measures are in place when deploying ESP32 in sensitive applications.

This chain involves the following actors

This following systems are involved

Attack entry point

Remediation actions

Exploitation actions

• https://github.com/TarlogicSecurity/Talks/blob/main/2025_RootedCon_BluetoothTools.pdf
• https://x.com/pascal_gujer/status/1898442439704158276
• https://www.tarlogic.com/news/backdoor-esp32-chip-infect-ot-devices/
• https://www.bleepingcomputer.com/news/security/undocumented-backdoor-found-in-bluetooth-chip-used-by-a-billion-devices/
• https://reg.rootedcon.com/cfp/schedule/talk/5
• https://flyingpenguin.com/?p=67838
• https://github.com/em0gi/CVE-2025-27840
• https://github.com/orgs/espruino/discussions/7699
• https://www.bleepingcomputer.com/news/security/undocumented-commands-found-in-bluetooth-chip-used-by-a-billion-devices/
• https://darkmentor.com/blog/esp32_non-backdoor/
• https://news.ycombinator.com/item?id=43308740
• https://news.ycombinator.com/item?id=43301369
• https://github.com/esphome/esphome/discussions/8382
• https://cheriot.org/auditing/backdoor/2025/03/09/no-esp32-style-backdoor.html
• https://www.espressif.com/en/news/Response_ESP32_Bluetooth