If you run ESPHome to manage your DIY smart home devices — Sonoff switches, custom sensors, ESP32-based automations — there’s a critical vulnerability you need to patch immediately.

CVE-2025-57808 is an authentication bypass flaw in ESPHome’s built-in web server component that makes the basic authentication on your devices completely ineffective. An attacker on the same local network doesn’t need your username or password. They can bypass the check entirely and do things like push custom OTA (over-the-air) firmware — replacing your legitimate device firmware with anything they want.

The vulnerability was discovered and reported by security researcher jesserockz and documented by GBHackers and Cyberpress. ESPHome maintainers released a patch in version 2025.8.1.

What Is ESPHome?

For readers who aren’t in the DIY smart home space: ESPHome is an open-source framework for programming ESP8266 and ESP32 microcontrollers — inexpensive Wi-Fi-enabled chips used in millions of consumer IoT devices and custom-built home automation sensors and switches.

ESPHome is widely used in the Home Assistant community. It lets you write device configuration in YAML, compile it, and flash it to your devices — then manage them wirelessly through over-the-air (OTA) updates. Devices typically run a small web server for management and status monitoring.

The affected component is that built-in web server and its authentication mechanism.

The Vulnerability: How Authentication Was Broken

The flaw exists in how ESPHome’s ESP-IDF platform implementation validates the HTTP Basic Authentication header.

When a client connects to the device’s web interface, it sends an Authorization header containing a base64-encoded string of username:password. The server is supposed to decode this, compare it to the stored credentials, and grant or deny access.

The bug is in that comparison logic:

Normal behavior (correct):

Client sends: Authorization: Basic dXNlcjpwYXNz  (base64 of "user:pass")
Server decodes: "user:pass"
Server compares entire string to stored credentials
Result: Match → grant access / No match → deny access

Vulnerable behavior (CVE-2025-57808):

Client sends: Authorization: Basic dXNl  (truncated base64)
Server decodes partial string: "user" 
Server compares ONLY the initial bytes of the supplied string
against the expected credential
If supplied fragment matches the PREFIX of the correct credential:
Result: GRANT ACCESS (incorrect)

Client sends: Authorization: Basic  (empty value)
Server receives empty Authorization header
Empty comparison against any string: no bytes to compare
Result: GRANT ACCESS (incorrect — even with no credentials at all)

The server grants access when the provided credential string is a prefix of the correct credential or when the Authorization header is completely empty. This makes the authentication trivially bypassable from any device on the local network.

What an Attacker Can Do

With authenticated access to an ESPHome device, an attacker on your Wi-Fi network can:

Push rogue OTA firmware: This is the most severe impact. Over-the-air firmware update replaces the entire firmware on the device. A malicious firmware update could:

  • Turn the device into a network pivot point
  • Capture and exfiltrate data flowing through connected sensors
  • Disable automations (turning off security cameras, unlocking doors in Home Assistant integrations)
  • Join the device to a botnet for DDoS participation
  • Create a persistent backdoor that survives factory reset attempts

Access device configuration: View all device settings, GPIO mappings, API keys, and automation logic stored on the device.

Manipulate device state: Trigger automations, switch outputs, read sensor data — depending on what the device controls.

Access any device on the local network that the ESP device can reach: Compromised devices can be used as stepping stones to other smart home devices.

Who Is Affected?

You are affected if:

  1. You are running ESPHome devices on the ESP-IDF platform (common on newer ESP32-based devices)
  2. You have web server component enabled in your ESPHome configuration
  3. You are running a version prior to 2025.8.1

The vulnerability is on the ESP-IDF platform specifically. The older Arduino framework platform uses a different web server implementation and is not affected by this specific flaw. However, it’s worth auditing your entire ESPHome deployment regardless.

How to Check Your Exposure

Check your ESPHome version: In the ESPHome dashboard (typically accessed through Home Assistant), look at the version listed for each device. Any device below 2025.8.1 needs updating.

Check your platform: In your device’s YAML configuration file, look for:

esp32:
  framework:
    type: esp-idf  # ← This is the affected platform

Check if web_server is enabled:

web_server:
  port: 80  # ← If this exists and you're on ESP-IDF, you're exposed

How to Patch

Update ESPHome to 2025.8.1 or later:

In the ESPHome dashboard:

  1. Go to the ESPHome dashboard
  2. Click the three-dot menu on an affected device
  3. Select “Install” → compile and flash the updated firmware

Or via command line:

pip install --upgrade esphome
esphome run your_device.yaml

If you cannot immediately update: As a temporary mitigation, consider:

  • Disabling the web_server: component in your device configuration and reflashing
  • Isolating your IoT VLAN to ensure ESPHome devices are not reachable from untrusted devices on your network
  • Using a firewall rule to block access to the device’s web server port (default 80) from unknown hosts

The Broader DIY Smart Home Security Lesson

CVE-2025-57808 is a reminder that the DIY smart home ecosystem — Home Assistant, ESPHome, Zigbee2MQTT, Node-RED, and similar tools — while incredibly powerful and privacy-preserving compared to cloud-dependent commercial alternatives, requires the operator to maintain security hygiene.

Commercial smart home devices from major vendors push updates automatically (for better or worse). DIY setups push updates when you push them. That’s a feature for control and privacy; it’s a responsibility for security.

A few practices that should become routine for DIY smart home users:

Subscribe to ESPHome release notes. The GitHub repository publishes release notes and security advisories. Follow it so you’re notified of security-relevant releases.

Segment your IoT network. Even if a device is compromised, network segmentation limits what an attacker can do with that foothold. Your ESPHome devices should not have direct network access to your computers, NAS, or other sensitive devices.

Audit your web_server: usage. The ESPHome web server is convenient for debugging and monitoring but creates attack surface. Consider whether you actually need it on production devices — if you only use the native ESPHome API for Home Assistant integration, you can disable the web server entirely.

Treat OTA access as a privilege. OTA updates are powerful — they replace firmware entirely. Protect the OTA mechanism with strong passwords and don’t expose OTA-capable devices to untrusted network segments.

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