A critical security vulnerability discovered in ESPHome’s web server component has exposed thousands of smart home devices to unauthorized access, effectively nullifying basic authentication protections on ESP-IDF platform implementations.
The flaw, designated CVE-2025-57808 with a CVSS score of 8.1, affects ESPHome version 2025.8.0 and allows attackers to bypass authentication mechanisms without any knowledge of legitimate credentials.
The vulnerability stems from a fundamental logic error in the HTTP basic authentication check within ESPHome’s web_server_idf component.
When processing authentication requests, the system’s AsyncWebServerRequest::authenticate function only compares bytes up to the length of the client-supplied authorization value, rather than validating the complete credential string.
This implementation flaw creates two distinct attack vectors that completely compromise device security.
The most severe aspect of this vulnerability involves empty authorization headers, where attackers can gain full access by simply sending a request with Authorization: Basic followed by an empty string.
GitHub analysts identified that this attack vector requires no prior knowledge of usernames or passwords, making it particularly dangerous for network-adjacent attackers.
Additionally, the flaw accepts partial password matches, meaning an attacker who discovers even a substring of the correct password can successfully authenticate.
Attack Mechanism and Technical Exploitation
The vulnerability’s technical foundation lies in the improper string comparison logic that processes base64-encoded credentials.
When a legitimate device is configured with credentials like user:somereallylongpass (encoded as dXNlcjpzb21lcmVhbGx5bG9uZ3Bhc3M=), the flawed authentication check accepts shorter strings such as dXNlcjpz (representing user:s) as valid credentials.
Practical exploitation requires minimal technical sophistication. Attackers can utilize simple curl commands to demonstrate the vulnerability:-
curl -D- -H 'Authorization: Basic ' http://target.local/This command bypasses authentication entirely, returning HTTP 200 responses instead of the expected 401 Unauthorized status.
The vulnerability becomes particularly concerning when Over-The-Air (OTA) update functionality is enabled, as attackers gain complete control over device firmware and configuration settings.
ESPHome addressed this critical flaw in version 2025.8.1, implementing proper credential validation that compares complete authorization strings rather than partial matches.
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