CVE-2023-41895 in Home Assistant
Summary
by MITRE • 10/25/2023
Home assistant is an open source home automation. 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 `` 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 Cross-site Scripting (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. This issue has been addressed in version 2023.9.0 and all users are advised to upgrade. There are no known workarounds for this vulnerability.
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Analysis
by VulDB Data Team • 11/11/2023
The vulnerability described in CVE-2023-41895 represents a critical cross-site scripting flaw in the Home Assistant open source home automation platform that stems from insufficient input validation during OAuth redirect URI processing. This vulnerability affects the authentication flow where users can log in to external websites using their Home Assistant credentials, with the system accepting redirect_uri and client_id parameters to facilitate this process. The core issue emerges from the inconsistent validation logic applied to different URI components during the authentication handshake, creating an exploitable gap in the security model.
The technical flaw manifests when Home Assistant processes the client_id parameter by fetching and inspecting HTML content from the specified URL to check for certain HTML tags, while simultaneously failing to apply the same scheme validation to the redirect_uri parameter. This discrepancy allows attackers to craft malicious redirect_uri values using the javascript: scheme, bypassing the normal validation that would otherwise prevent such dangerous URI schemes from being processed. The vulnerability specifically leverages the fact that while the system validates that redirect_uri schemes are either http or https, it does not perform the same validation on the client_id URLs that are fetched and analyzed for HTML content, creating a pathway for arbitrary JavaScript execution within the Home Assistant administrative context.
The operational impact of this vulnerability is severe and potentially catastrophic for Home Assistant installations, as it enables full account takeover and complete system compromise. When exploited, the XSS vulnerability allows attackers to execute malicious JavaScript code within the Home Assistant frontend domain, potentially gaining access to all administrative functions, user credentials, and system configuration data. This vulnerability could be particularly dangerous in home automation environments where Home Assistant controls critical systems such as lighting, security cameras, door locks, and environmental controls, making it a prime target for attackers seeking to gain unauthorized access to physical security systems and personal data.
The vulnerability aligns with CWE-79 Cross-site Scripting and follows ATT&CK techniques related to initial access and privilege escalation through web application vulnerabilities. The flaw demonstrates poor input validation and insufficient sanitization of user-provided URI parameters, creating an attack surface that directly enables code execution in the context of the authenticated user's session. Organizations using Home Assistant versions prior to 2023.9.0 face significant risk of unauthorized access and potential system compromise, with no viable workarounds available since the vulnerability exists at the core authentication processing logic. The fix implemented in version 2023.9.0 addresses this by ensuring consistent validation of all URI schemes and preventing the execution of dangerous JavaScript URIs during the client_id processing phase, thereby closing the XSS attack vector that previously allowed arbitrary code execution in the administrative context of the Home Assistant platform.