CVE-2026-64823: XSS (CVSS 4.7)

Description

Home Assistant Core before 2026.5.4 contains a cross-site scripting vulnerability in the Shelly integration's async_get_media_image() method that allows attackers controlling a Shelly device's thumb field to serve arbitrary HTML content by supplying a data URI with a text/html content type without validation against an image-only allowlist. Attackers can cause the media player proxy endpoint to serve attacker-controlled bytes with Content-Type text/html in the Home Assistant web origin, enabling theft of session tokens from local storage and authenticated calls to sensitive service endpoints including lock, alarm, and cover controls.

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CVSS v3.1 Score

4.7

MEDIUM

CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:N

Weakness Type (CWE)

CWE-79 Cross-site Scripting (XSS)

References

Other References

https://github.com/home-assistant/core/commit/894a68acb678afc382fe5ea9002e61ab7f862011 https://github.com/home-assistant/core/pull/171585 https://github.com/home-assistant/core/releases/tag/2026.5.4 https://www.vulncheck.com/advisories/home-assistant-core-xss-via-shelly-media-player-py-thumb-uri

Frequently Asked Questions

What is CVE-2026-64823? +

Home Assistant Core before 2026.5.4 contains a cross-site scripting vulnerability in the Shelly integration's async_get_media_image() method that allows attackers controlling a Shelly device's thumb field to serve arbitrary HTML content by supplying a data URI with a text/html content type without validation against an image-only allowlist. Attackers can cause the media player proxy endpoint to serve attacker-controlled bytes with Content-Type text/html in the Home Assistant web origin, enabling theft of session tokens from local storage and authenticated calls to sensitive service endpoints including lock, alarm, and cover controls. It has a CVSS v3.1 base score of 4.7 (MEDIUM).

How severe is CVE-2026-64823? +

CVE-2026-64823 has a CVSS v3.1 score of 4.7 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance.

How do I check if I'm vulnerable to CVE-2026-64823? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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CVE-2026-64823