How severe is CVE-2021-41104?

CVE-2021-41104 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.

Is CVE-2021-41104 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (66th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-41104?

CVE-2021-41104 affects Esphome Esphome Firmware. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-41104?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-41104 published?

CVE-2021-41104 was published on 2021-09-28 and last updated on 2026-06-17.

CVE-2021-41104

CVE-2021-41104 is a high-severity vulnerability in Esphome Esphome Firmware with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-306.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 4.3
EPSS exploit prediction: 1% (66th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-306
Affected product: Esphome Esphome Firmware
Published: 2021-09-28
Last modified: 2026-06-17

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`.

Frequently asked questions

What is 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`.
How severe is CVE-2021-41104?: CVE-2021-41104 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.
Is CVE-2021-41104 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (66th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-41104?: CVE-2021-41104 affects Esphome Esphome Firmware. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-41104?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-41104 published?: CVE-2021-41104 was published on 2021-09-28 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:o:esphome:esphome_firmware:*:*:*:*:*:*:*:*

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