ghsa-mxh2-ccgj-8635
Vulnerability from github
Summary
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:
yaml
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 ... ```
Impact
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.
Remediation
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.
{
"affected": [
{
"database_specific": {
"last_known_affected_version_range": "\u003c= 2025.8.0"
},
"package": {
"ecosystem": "PyPI",
"name": "esphome"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "2025.8.1"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2025-57808"
],
"database_specific": {
"cwe_ids": [
"CWE-187",
"CWE-303"
],
"github_reviewed": true,
"github_reviewed_at": "2025-09-02T16:46:58Z",
"nvd_published_at": "2025-09-02T01:15:29Z",
"severity": "HIGH"
},
"details": "### Summary\nOn the ESP-IDF platform, ESPHome\u0027s [`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`\u0027s [`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\u0027t 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 \u0027Authorization: Basic \u0027 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.",
"id": "GHSA-mxh2-ccgj-8635",
"modified": "2025-09-02T16:46:58Z",
"published": "2025-09-02T16:46:58Z",
"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"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N",
"type": "CVSS_V3"
}
],
"summary": "ESP-IDF web_server basic auth bypass using empty or incomplete Authorization header"
}
Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
- Confirmed: The vulnerability is confirmed from an analyst perspective.
- Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
- Patched: This vulnerability was successfully patched by the user reporting the sighting.
- Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
- Not confirmed: The user expresses doubt about the veracity of the vulnerability.
- Not patched: This vulnerability was not successfully patched by the user reporting the sighting.