What’s Vulnerable › Vulnerabilities

CVE-2021-41104: web_server allows OTA update without checking user defined basic auth username & password

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-09-28 · updated 2026-06-17
• Weakness: CWE-306

Description

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`.

Affected products

• Esphome Firmware: before 2021.9.2 — fixed in 2021.9.2

How to fix

Upgrade to a fixed version: Esphome Firmware 2021.9.2. Check the vendor advisory for mitigations.

References

• https://github.com/esphome/esphome/pull/2409/commits/207cde1667d8c799a197b78ca8a5a14de8d5ca1e
• https://github.com/esphome/esphome/releases/tag/2021.9.2
• https://github.com/esphome/esphome/security/advisories/GHSA-48mj-p7x2-5jfm
• https://github.com/esphome/esphome/pull/2409/commits/207cde1667d8c799a197b78ca8a5a14de8d5ca1e
• https://github.com/esphome/esphome/releases/tag/2021.9.2
• https://github.com/esphome/esphome/security/advisories/GHSA-48mj-p7x2-5jfm

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