CVE-2021-41104

web_server allows OTA update without checking user defined basic auth username & password

7.5 HighFix available

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.

Attack profile

How easy it is to exploit

Attack vector: Network
Complexity: Low
Privileges needed: None
User interaction: None

What an attacker can affect

Confidentiality: None
Integrity: High
Availability: None

Exploit likelihood

1.21%Up 0.3 points since Sep 29, 2021

What each source reports

CVE List Score used 7.5

web_server allows OTA update without checking user defined basic auth username & password

Record: CVE-2021-41104
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Weakness: CWE-306
Updated: 2026-11-02

EUVDEUVD-2021-0071 7.5

Record: EUVD-2021-0071
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Updated: 2026-11-03

GitHub AdvisoriesGHSA-48mj-p7x2-5jfm 8.7

Basic auth bypass in esphome

Impact

Anyone with web_server enabled and HTTP basic auth configured on 2021.9.1 or older

web_server allows OTA update without checking user defined basic auth username & password

Patches

Patch released in 2021.9.2

Workarounds

Disable/remove web_server

Record: GHSA-48mj-p7x2-5jfm
CVSS 4.0: 8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Weakness: CWE-306
Updated: 2026-11-02

NVD 7.5

Record: CVE-2021-41104
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
CVSS 2.0: 4.3 MediumAV:N/AC:M/Au:N/C:N/I:P/A:N
Weakness: CWE-306
Updated: 2026-11-02

OSVGHSA-48mj-p7x2-5jfm 8.7

Basic auth bypass in esphome

Impact

Anyone with web_server enabled and HTTP basic auth configured on 2021.9.1 or older

web_server allows OTA update without checking user defined basic auth username & password

Patches

Patch released in 2021.9.2

Workarounds

Disable/remove web_server

Record: GHSA-48mj-p7x2-5jfm
CVSS 4.0: 8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Weakness: CWE-306
Updated: 2026-11-02

OSVPYSEC-2021-351 No score

Record: PYSEC-2021-351
Updated: 2026-11-02

Affected products

Affected packages

Affected packages
Package	Affected	Fixed
`esphome` PyPI	before 2021.9.2	2021.9.2
`esphome` PyPI	before 2021.9.2, plus listed versions 1.10.11.11.01.11.0b11.11.0b21.11.0b3 Show 45 moreShow less 1.11.11.11.21.12.01.12.0b11.12.0b21.12.0b31.12.0b41.12.11.12.21.13.01.13.0b11.13.0b21.13.0b31.13.0b41.13.0b51.13.0b61.13.0b71.13.11.13.21.13.31.13.41.13.51.13.61.14.01.14.0b11.14.0b21.14.0b31.14.0b41.14.0b51.14.11.14.21.14.31.14.41.14.51.15.01.15.0b11.15.0b21.15.0b31.15.0b41.15.11.15.21.15.31.16.01.16.0b11.16.0b2	2021.9.2

History

History
Recorded	Changed	Sources
Nov 3, 2026	aliases	EUVD
Nov 2, 2026	first indexed	CVE List, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2021-41104 is a high vulnerability (CVSS 7.5) in Esphome, published September 28, 2021. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 1.21%, the 68th percentile. Fixed in esphome 2021.9.2.

References

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This page doesn't list everything

Left out here: 53 versions. The JSON record has them.