ESPHome vulnerable to denial-of-service via out-of-bounds check bypass in the API component
Summary
An integer overflow in the API component's protobuf decoder allows denial-of-service attacks when API encryption is not used.
Details
The bounds check ptr + field_length > end in components/api/proto.cpp can overflow when a malicious client sends a large field_length value. This affects all ESPHome device platforms (ESP32, ESP8266, RP2040, LibreTiny). The overflow bypasses the out-of-bounds check, causing the device to read invalid memory and crash.
When using the plaintext API protocol, this attack can be performed without authentication. When noise encryption is enabled, knowledge of the encryption key is required.
Affected Versions
ESPHome 2025.9.0 through 2025.12.6
Mitigation
- Upgrade to ESPHome 2025.12.7 or later (or 2026.1.0b3 or later)
- Enable API encryption with a unique key per device
- Follow the Security Best Practices
Severity
Low - Users following Security Best Practices with API encryption enabled are not affected without knowledge of the encryption key.
Impact
Denial-of-service. An attacker with network access to port 6053 can crash and reboot the device.
Credits
Thanks to @Mat931 for responsibly reporting this vulnerability.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | esphome | >= 2025.9.0, < 2025.12.7 | 2025.12.7 |
References
- https://github.com/esphome/esphome/security/advisories/GHSA-4h3h-63v6-88qx
- https://nvd.nist.gov/vuln/detail/CVE-2026-23833
- https://github.com/esphome/esphome/pull/13306
- https://github.com/esphome/esphome/commit/69d7b6e9210390051318bd8e6410727689de08d6
- https://esphome.io/guides/security_best_practices
- https://github.com/esphome/esphome
- https://pypi.org/project/esphome
- https://github.com/advisories/GHSA-4h3h-63v6-88qx
- CVSS vector
CVSS:4.0/AV:A/AC:L/AT:N/PR:H/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N- Weakness (CWE)
CWE-190- Platform
- Python (PyPI)
- Package
esphome- Disclosed
- 21.01.2026
- Updated
- 11.10.2026 13:18
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-1326 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-4h3h-63v6-88qx - CC BY 4.0
Vulnerability history: esphome
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 6
- First → latest
- 09.2021 01.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 4
- Medium 2
Disclosures per year
- 2021: 1
- 2022: 0
- 2023: 0
- 2024: 3
- 2025: 1
- 2026: 1
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ESPHome vulnerable to denial-of-service via out-of-bounds check bypass in the API component this entry
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