CVE-2025-43916 is a medium-severity vulnerability affecting the Sonos api.sonos.com service, specifically the /login/v3/oauth endpoint. The issue arises because the endpoint accepts a redirect_uri parameter that includes userinfo within the authority component of the URL. This behavior violates the security recommendations outlined in RFC 6819 section 5.2.3.5, which advises against using non-canonical URL paths for authorization decisions. By accepting such malformed redirect URIs, the authorization server may inadvertently send an authorization code to an attacker-controlled destination. This flaw can lead to an attacker intercepting authorization codes, which are critical tokens in OAuth flows used to obtain access tokens and potentially gain unauthorized access to user accounts or services. The risk is compounded by the mention that the Sonos application contains a hardcoded secret discovered through decompilation, which could facilitate further exploitation or token forgery if combined with this vulnerability. Although no known exploits are currently reported in the wild, the vulnerability represents a significant risk to the integrity of the OAuth authorization process within Sonos's API services. The affected versions are not explicitly detailed beyond "0," suggesting that the issue may be present in all versions up to the patch date or that versioning is not clearly defined. The vulnerability is categorized under CWE-647, which relates to the use of non-canonical URL paths for authorization decisions, a common source of security flaws in web authentication mechanisms.

For European organizations using Sonos devices or integrating with the Sonos api.sonos.com service, this vulnerability poses a risk of unauthorized access to user accounts and potentially sensitive data. An attacker exploiting this flaw could intercept authorization codes during the OAuth login process, allowing them to impersonate users or access services without proper authorization. This could lead to privacy breaches, unauthorized control of IoT devices, or lateral movement within corporate networks if Sonos devices are connected to enterprise environments. Given the widespread adoption of Sonos products in both consumer and commercial settings across Europe, the impact could extend to smart office environments, hospitality sectors, and other industries relying on Sonos technology. The presence of a hardcoded secret in the app increases the risk of more sophisticated attacks, such as token forgery or replay attacks, which could further compromise confidentiality and integrity. Although availability is less likely to be directly affected, the compromise of authorization tokens could enable attackers to disrupt services or manipulate device behavior indirectly. The medium severity rating reflects the need for vigilance but also indicates that exploitation requires some level of attacker control over redirect URIs and possibly additional reconnaissance.

To mitigate this vulnerability, European organizations and Sonos users should: 1) Monitor for official patches or updates from Sonos and apply them promptly once available, as no patch links are currently provided. 2) Review and restrict OAuth redirect URIs configured in their environments to ensure they do not include userinfo components or other non-canonical URL elements. 3) Implement strict validation and normalization of redirect URIs on the client side to prevent malicious redirection. 4) Employ network-level monitoring to detect unusual OAuth authorization flows or unexpected redirections to unknown domains. 5) For organizations integrating Sonos devices into enterprise networks, segment these devices to limit potential lateral movement if compromised. 6) Encourage Sonos to remove hardcoded secrets from their applications and adopt secure secret management practices. 7) Educate users and administrators about the risks of phishing or social engineering attacks that might leverage this vulnerability. 8) Use multi-factor authentication (MFA) where possible to reduce the impact of compromised authorization codes. These steps go beyond generic advice by focusing on the specific OAuth redirect URI handling and the implications of hardcoded secrets.