Part of the Cure53 security audit of Home Assistant.
The test team noted that the Home Assistant login page allows users to use their local Home Assistant credentials and log in to another website that specifies the redirect_uri and client_id parameters.
Although the redirect_uri validation typically ensures that it matches the client_id and the scheme represents either http or https, Home Assistant will fetch the client_id and check for <link rel="redirect_uri" href="..."> HTML tags on the page. These URLs are not subjected to the same scheme validation and thus allow for arbitrary JavaScript execution on the Home Assistant administration page via usage of javascript: scheme URIs.
This XSS vulnerability can be executed on the Home Assistant frontend domain, which may be used for a full takeover of the Home Assistant account and installation.
To mitigate this issue, Cure53 recommends ensuring that the redirect_uri value uses either the http or https scheme. Additionally, the developer team could incorporate a CSP into Home Assistant to mitigate the risk of similar XSS attacks in the future, especially on sensitive pages.
Part of the Cure53 security audit of Home Assistant.
The test team noted that the Home Assistant login page allows users to use their local Home Assistant credentials and log in to another website that specifies the
redirect_uriandclient_idparameters.Although the
redirect_urivalidation typically ensures that it matches theclient_idand the scheme represents eitherhttporhttps, Home Assistant will fetch theclient_idand check for<link rel="redirect_uri" href="...">HTML tags on the page. These URLs are not subjected to the same scheme validation and thus allow for arbitrary JavaScript execution on the Home Assistant administration page via usage ofjavascript:scheme URIs.This XSS vulnerability can be executed on the Home Assistant frontend domain, which may be used for a full takeover of the Home Assistant account and installation.
To mitigate this issue, Cure53 recommends ensuring that the
redirect_urivalue uses either thehttporhttpsscheme. Additionally, the developer team could incorporate a CSP into Home Assistant to mitigate the risk of similar XSS attacks in the future, especially on sensitive pages.