What is CVE-2021-41104?

CVE-2021-41104 is a high-severity vulnerability in Esphome, classified under Missing Authentication for Critical Function. CVSS score: 7.5/10. Published 2021-09-28.

How severe is CVE-2021-41104?

High severity. CVSS v3 base score is 7.5 out of 10.

Auth bypass in Esphome

CVE-2021-41104

ESPHome is a system to control the ESP8266/ESP32. Anyone with web_server enabled and HTTP basic auth configured on version 2021.9.1 or older is vulnerable to an issue in which `web_server` allows over-the-air (OTA) updates without checking user defined basic auth username & password. This issue is patched in version 2021.9.2. As a workaround, one may disable or remove `web_server`.

Vulnerability class: Broken Authentication

Published 2021-09-28 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N.

EPSS exploit prediction

EPSS: 0.012 (67.2th percentile), scored 2026-09-25.

Low probability of exploitation in the next 30 days, but still tracked. 67th percentile — 67.2% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.012 · newest: 0.012 · change: 0.000

Affected products

Weakness classification (CWE)

CWE-306 — Missing Authentication for Critical Function

References

github.com/esphome/esphome/security/advisories/GHSA-48mj-p7x2-5jfm (Patch, Third Party Advisory)
github.com/esphome/esphome/pull/2409/commits/207cde1667d8c799a197b78ca8a5a14de8… (Patch, Third Party Advisory)
github.com/esphome/esphome/releases/tag/2021.9.2 (Third Party Advisory, Release Notes)

Frequently asked questions

What is CVE-2021-41104?: CVE-2021-41104 is a high-severity vulnerability in Esphome, classified under Missing Authentication for Critical Function. CVSS score: 7.5/10. Published 2021-09-28.
How severe is CVE-2021-41104?: High severity. CVSS v3 base score is 7.5 out of 10.