CVE-2023-41893 in Home Assistant
Summary
by MITRE • 10/25/2023
Home assistant is an open source home automation. The audit team’s analyses confirmed that the `redirect_uri` and `client_id` are alterable when logging in. Consequently, the code parameter utilized to fetch the `access_token` post-authentication will be sent to the URL specified in the aforementioned parameters. Since an arbitrary URL is permitted and `homeassistant.local` represents the preferred, default domain likely used and trusted by many users, an attacker could leverage this weakness to manipulate a user and retrieve account access. Notably, this attack strategy is plausible if the victim has exposed their Home Assistant to the Internet, since after acquiring the victim’s `access_token` the adversary would need to utilize it directly towards the instance to achieve any pertinent malicious actions. To achieve this compromise attempt, the attacker must send a link with a `redirect_uri` that they control to the victim’s own Home Assistant instance. In the eventuality the victim authenticates via said link, the attacker would obtain code sent to the specified URL in `redirect_uri`, which can then be leveraged to fetch an `access_token`. Pertinently, an attacker could increase the efficacy of this strategy by registering a near identical domain to `homeassistant.local`, which at first glance may appear legitimate and thereby obfuscate any malicious intentions. 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-2023-41893 represents a critical authorization flow weakness within the Home Assistant open source home automation platform. This security flaw exists in the OAuth 2.0 authentication implementation where the redirect_uri and client_id parameters can be manipulated during the login process. The issue stems from insufficient validation of these parameters, allowing attackers to specify arbitrary redirect URLs that will receive the authorization code during the authentication flow. This fundamental flaw in the authentication mechanism creates a pathway for sophisticated social engineering attacks that can compromise user accounts and potentially lead to full system compromise.
The technical exploitation of this vulnerability follows a precise attack pattern that leverages the trust relationship between users and the default homeassistant.local domain. When users authenticate with their Home Assistant instance, the system accepts attacker-controlled redirect_uri values that can point to malicious domains controlled by threat actors. The authorization code, which serves as a temporary credential for obtaining access tokens, gets redirected to these attacker-controlled endpoints. This creates a man-in-the-middle scenario where attackers can intercept the authorization code and subsequently exchange it for a legitimate access_token through the OAuth 2.0 token endpoint. The vulnerability is particularly dangerous because the default homeassistant.local domain is trusted by users, making social engineering attacks more effective when attackers register domains that closely resemble the legitimate one. This attack vector directly violates the principle of least privilege and authorization security by allowing unauthorized parties to obtain valid authentication tokens without proper verification.
The operational impact of CVE-2023-41893 extends beyond simple credential theft, as successful exploitation enables attackers to perform administrative actions within the compromised Home Assistant instance. Once an attacker obtains a valid access_token, they can make authenticated requests to the Home Assistant API, potentially gaining access to sensitive home automation data, controlling connected devices, and modifying system configurations. The vulnerability is particularly concerning for users who expose their Home Assistant instances to the internet, as it eliminates the need for physical access or complex network-level attacks. The attack requires only successful social engineering to convince victims to click on malicious links, making it extremely difficult to detect and prevent. The security implications align with CWE-384, which addresses session fixation vulnerabilities, and can be categorized under ATT&CK technique T1566 for social engineering attacks that leverage credential harvesting.
The mitigation strategy for this vulnerability involves upgrading to Home Assistant version 2023.9.0 or later, which implements proper validation of redirect_uri parameters to prevent arbitrary URL redirection. This fix aligns with security best practices for OAuth 2.0 implementations that require strict validation of redirect URIs against a pre-approved whitelist. Organizations should also consider implementing additional security measures such as monitoring for unauthorized domain registrations that might be used in similar attacks, conducting security awareness training for users about suspicious authentication links, and ensuring that Home Assistant instances are not unnecessarily exposed to the public internet. The vulnerability demonstrates the importance of proper input validation in authentication flows and serves as a reminder that even open source systems can contain critical flaws that require immediate attention and patching to maintain security integrity.