CVE-2026-23833

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.

• CWE-190

• https://esphome.io/guides/security_best_practicesTechnical Description
• https://github.com/esphome/esphome/commit/69d7b6e9210390051318bd8e6410727689de08d6Patch
• https://github.com/esphome/esphome/pull/13306Issue Tracking, Patch
• https://github.com/esphome/esphome/security/advisories/GHSA-4h3h-63v6-88qxMitigation, Patch, Vendor Advisory

Published

Jan 19, 2026

Last Modified

Jun 17, 2026

Status

Analyzed

• How Strix found a critical auth bypass in etcdStrix autonomously discovered a critical authentication bypass in etcd, later designated CVE-2026-33413.
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