---
id: CVE-2026-23833
aliases:
  - GHSA-4h3h-63v6-88qx
  - PYSEC-2026-1326
title: >-
  ESPHome vulnerable to denial-of-service via out-of-bounds check bypass in the
  API component
summary: >-
  ESPHome vulnerable to denial-of-service via out-of-bounds check bypass in the
  API component
severity: medium
vendor: esphome
product: esphome
ecosystem: pip
affected:
  - 'esphome >= 2025.9.0, < 2025.12.7'
patched:
  - esphome 2025.12.7
published: '2026-01-21'
updated: '2026-07-07'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-4h3h-63v6-88qx'
references:
  - url: 'https://github.com/esphome/esphome/security/advisories/GHSA-4h3h-63v6-88qx'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-23833'
  - url: 'https://github.com/esphome/esphome/pull/13306'
  - url: >-
      https://github.com/esphome/esphome/commit/69d7b6e9210390051318bd8e6410727689de08d6
  - url: 'https://esphome.io/guides/security_best_practices'
  - url: 'https://github.com/esphome/esphome'
tags:
  - osv
  - pip
epss: 0.00305
epssPercentile: 0.20644
ingestedAt: '2026-07-08T18:25:45.489Z'
---

## Overview

### 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](https://esphome.io/components/api.html#configuration-variables) with a unique key per device
- Follow the [Security Best Practices](https://esphome.io/guides/security_best_practices/)

### Severity
Low - Users following [Security Best Practices](https://esphome.io/guides/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](https://github.com/Mat931) for responsibly reporting this vulnerability.

## Affected packages

- `esphome >= 2025.9.0, < 2025.12.7`

## Remediation

Upgrade to a patched release:

- `esphome 2025.12.7`