Smart Home Devices at Risk – ESPHome Web Server Flaw Lets Hackers Bypass Authentication

A critical vulnerability has been discovered in the ESPHome web server component on the ESP-IDF platform, allowing unauthorized access to smart home devices without valid credentials.

The flaw’s root cause is the improper handling of the HTTP Basic Authentication header, which effectively nullifies authentication on affected devices.

Prefix-Based Authentication Bypass

ESPHome’s web_server component uses the AsyncWebServerRequest::authenticate method to validate client-supplied credentials via the Authorization: Basic <base64(user:pass)> header.

However, the implementation on ESP-IDF platforms compares only a prefix of the correct base64-encoded credentials up to the length of the client’s supplied value. As a result, any prefix of the actual credential string, including an empty string, will pass the check.

For instance, the valid credentials:

textdXNlcjpzb21lcmVhbGx5bG9uZ3Bhc3M=

(user:somereallylongpass)

can be bypassed by supplying:

textdXNlcjpz

(user:s)

or even no value at all (Authorization: Basic ). This trivial manipulation grants full access to the web server interface, including Over-the-Air (OTA) update functionality if enabled. A simple curl The command illustrates the issue:

bash# Unauthorized initial response
$ curl -D- http://example.local/
HTTP/1.1 401 Unauthorized

# Bypass with empty credentials
$ curl -D- -H 'Authorization: Basic ' http://example.local/
HTTP/1.1 200 OK

No username or password knowledge is required, and brute-forcing is unnecessary, enabling any local network device to perform unauthorized actions, alter device states, or inject malicious firmware.

Security Implications and Remediation

This vulnerability undermines the security model of smart home deployments by permitting unauthenticated control of lights, locks, sensors, and other ESPHome-managed peripherals.

When OTA updates are exposed via the web_server component, attackers can deploy malicious firmware, compromising privacy, safety, and broader network integrity.

The issue is resolved in ESPHome 2025.8.1 and later, where the whole base64-encoded credential string is strictly validated. Until devices are updated, it is recommended to:

• Disable the web_server component on ESP-IDF–based devices, especially if OTA is enabled.
• Use the captive_portal component for OTA updates, which enforces proper authentication.
• Implement network controls such as firewall rules or VLAN segmentation to restrict access to management interfaces.

Manufacturers and integrators should prompt users to apply updates immediately. Maintaining up-to-date software and enforcing strong network segmentation are critical to safeguarding connected home environments.

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