CVE-2025-57808: Esphome ESP-IDF Web_server Basic Auth Bypass Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-mxh2-ccgj-8635",
  "modified" : "2025-09-02T16:46:58Z",
  "published" : "2025-09-02T16:46:58Z",
  "aliases" : [ "CVE-2025-57808" ],
  "summary" : "ESP-IDF web_server basic auth bypass using empty or incomplete Authorization header",
  "details" : "### Summary\nOn the ESP-IDF platform, ESPHome's [`web_server` authentication](https://esphome.io/components/web_server.html#configuration-variables) 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.\n\n### Details\nThe HTTP basic auth check in `web_server_idf`'s [`AsyncWebServerRequest::authenticate`](https://github.com/esphome/esphome/blob/ef2121a215890d46dc1d25ad363611ecadc9e25e/esphome/components/web_server_idf/web_server_idf.cpp#L256) 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`).\n\nFurthermore, 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`).\n\n### PoC\nConfigure ESPHome as follows:\n\n```yaml\nesp32:\n  board: ...\n  framework:\n    type: esp-idf\nweb_server:\n  auth:\n    username: user\n    password: somereallylongpass\n```\n\nIn 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`.)\n\nYou 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:\n\n```\n$ curl -D- http://example.local/\nHTTP/1.1 401 Unauthorized\n...\n\n$ curl -D- -H 'Authorization: Basic ' http://example.local/\nHTTP/1.1 200 OK\n...\n```\n\n### Impact\nThis 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.\n\n### Remediation\nThis vulnerability is fixed in 2025.8.1 and later.\n\nFor older versions, disabling the `web_server` component on ESP-IDF devices may be prudent, particularly if OTA updates through `web_server` are enabled.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "esphome"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2025.8.1"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 2025.8.0"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/esphome/esphome/security/advisories/GHSA-mxh2-ccgj-8635"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2025-57808"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/esphome/esphome/commit/2aceb56606ec8afec5f49c92e140c8050a6ccbe5"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/esphome/esphome"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-187", "CWE-303" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2025-09-02T16:46:58Z",
    "nvd_published_at" : "2025-09-02T01:15:29Z"
  }
}