CVE-2026-23833 ESPHome vulnerable to denial-of-service via out-of-bounds check bypass in the API component

What is CVE-2026-23833?

CVE-2026-23833 is a low-severity vulnerability in esphome, published on 19 Jan 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

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.

Weakness: CWE-190

Which versions are affected by CVE-2026-23833?

3 open source packages ship an affected version, including esphome. It affects 1 product.

Products include Esphome Esphome.

How do I fix CVE-2026-23833?

Upgrade esphome to 2025.12.7 or later.

Is CVE-2026-23833 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-23833 exists.

Other vulnerabilities in esphome

• CVE-2024-27081 ESPHome remote code execution via arbitrary file write High 7.2
• CVE-2024-27287 ESPHome vulnerable to stored Cross-site Scripting in edit configuration file API Medium 6.5

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-4h3h-63v6-88qx, PYSEC-2026-1326.