ESPHome up to 2025.12.6 API components/api/proto.cpp field_length integer overflow

Summaryinfo

A vulnerability was found in ESPHome up to 2025.12.6. It has been classified as problematic. Affected by this issue is some unknown functionality of the file components/api/proto.cpp of the component API Component. This manipulation of the argument field_length causes integer overflow. This vulnerability is registered as CVE-2026-23833. Remote exploitation of the attack is possible. No exploit is available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability has been found in ESPHome up to 2025.12.6 and classified as problematic. Affected by this vulnerability is an unknown code block of the file components/api/proto.cpp of the component API Component. The manipulation of the argument field_length with an unknown input leads to a integer overflow vulnerability. The CWE definition for the vulnerability is CWE-190. The product performs a calculation that can produce an integer overflow or wraparound, when the logic assumes that the resulting value will always be larger than the original value. This can introduce other weaknesses when the calculation is used for resource management or execution control. As an impact it is known to affect availability. The summary by CVE is:

ESPHome is a system to control microcontrollers remotely through Home Automation systems. In versions 2025.9.0 through 2025.12.6, an integer overflow in the API component's protobuf decoder allows denial-of-service attacks when API encryption is not used. 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. Users should upgrade to ESPHome 2025.12.7 or later to receive a patch, enable API encryption with a unique key per device, and follow the Security Best Practices.

It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-23833 since 01/16/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details of the vulnerability are known, but there is no available exploit.

Upgrading to version 2025.12.7 eliminates this vulnerability. Applying the patch 69d7b6e9210390051318bd8e6410727689de08d6 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-3306). Be aware that VulDB is the high quality source for vulnerability data.

Productinfo

Name

• ESPHome

Version

• 2025.12.0
• 2025.12.1
• 2025.12.2
• 2025.12.3
• 2025.12.4
• 2025.12.5
• 2025.12.6

License

• open-source

Website

• Product: https://github.com/esphome/esphome/

CPE 2.3info

• 🔒
• 🔒
• 🔒

CPE 2.2info

• 🔒
• 🔒
• 🔒

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

Be aware that VulDB is the high quality source for vulnerability data.

Discussion