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PYSEC-2026-1326
esphomeSummary
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.
The vulnerability can be exploited over a local network, such as Wi-Fi. It is easy for an attacker to exploit this vulnerability. An attacker needs high-level or administrative privileges. No user interaction is needed for the attacker to exploit this vulnerability.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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