CVE-2025-57808

On the ESP-IDF platform, ESPHome's web_server authentication check can pass incorrectly when the client-supplied base64-encoded Authorization value is empty or is a substring of the correct value (e.g., correct username with partial password). This allows access to web_server functionality (including OTA, if enabled) without knowing any information about the correct username or password.

Details

The HTTP basic auth check in web_server_idf's AsyncWebServerRequest::authenticate only compares up to auth.value().size() - auth_prefix_len bytes of the base64-encoded user:pass string. This means a client-provided valuer like dXNlcjpz (user:s) will pass the check when the correct value is much longer, e.g., dXNlcjpzb21lcmVhbGx5bG9uZ3Bhc3M= (user:somereallylongpass).

Furthermore, the check will also pass when the supplied value is the empty string, which removes the need to know (or brute force) the username. A browser won't generally issue such a request, but it can easily be done by manually constructing the Authorizaztion request header (e.g., via curl).

PoC

Configure ESPHome as follows:

esp32:
  board: ...
  framework:
    type: esp-idf
web_server:
  auth:
    username: user
    password: somereallylongpass

In a browser, you can correctly log in by supplying username user and password somereallylongpass... but you can also incorrectly log in by supplying substrings of the password whose base64-encoded digest matches a prefix of the correct digest. (For example, I was able to log into an ESPHome device so configured by supplying password some... or even just s.)

You can also use a tool like curl to manually set an Authorization request header that always passes the check without any knowledge of the username:

$ curl -D- http://example.local/
HTTP/1.1 401 Unauthorized
...

$ curl -D- -H 'Authorization: Basic ' http://example.local/
HTTP/1.1 200 OK
...

This vulnerability effectively nullifies basic auth support for the ESP-IDF web_server, allowing auth bypass from another device on the local network with no knowledge of the correct username or password required.

CVE-2025-57808 has a CVSS score of 8.1 (High). The vector is reachable from an adjacent network, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2025.8.1); upgrading removes the vulnerable code path.

Kodem intelligence

This vulnerability is fixed in 2025.8.1 and later.

For older versions, disabling the web_server component on ESP-IDF devices may be prudent, particularly if OTA updates through web_server are enabled.

1. What is CVE-2025-57808? CVE-2025-57808 is a high-severity security vulnerability in esphome (pip), affecting versions <= 2025.8.0. It is fixed in 2025.8.1.
2. How severe is CVE-2025-57808? CVE-2025-57808 has a CVSS score of 8.1 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of esphome are affected by CVE-2025-57808? esphome (pip) versions <= 2025.8.0 is affected.
4. Is there a fix for CVE-2025-57808? Yes. CVE-2025-57808 is fixed in 2025.8.1. Upgrade to this version or later.
5. Is CVE-2025-57808 exploitable, and should I be worried? Whether CVE-2025-57808 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2025-57808 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2025-57808? Upgrade esphome to 2025.8.1 or later.