CVE-2021-41180 is a security vulnerability classified as an open redirect (CWE-601) affecting the Nextcloud Talk Android client versions prior to 12.1.2. Nextcloud Talk is a self-hosted messaging and collaboration service widely used for secure communication. The vulnerability arises due to insufficient validation of URLs used in the geolocation preview feature within the Android Talk application. Specifically, an attacker can manipulate the link associated with a geolocation preview, causing the application to redirect users to an untrusted external site. This open redirect flaw can be exploited by crafting malicious links that appear legitimate within the app, potentially facilitating phishing attacks or redirecting users to malicious websites. However, exploitation requires user interaction, meaning the user must click on the manipulated geolocation preview link for the redirect to occur. The vulnerability does not affect other Nextcloud Talk clients or versions beyond 12.1.2, and there are no known workarounds aside from upgrading the app. No known exploits have been reported in the wild. The vulnerability impacts confidentiality and integrity indirectly by enabling social engineering attacks but does not directly compromise system availability or data integrity. The lack of URL validation is a common security oversight that can be leveraged to bypass user trust and redirect users to harmful sites, potentially leading to credential theft or malware infection if users are deceived. The fix involves updating the Nextcloud Talk Android client to version 12.1.2 or later, where proper validation of geolocation preview URLs has been implemented to prevent open redirects.

For European organizations using Nextcloud Talk Android clients, this vulnerability poses a moderate risk primarily through social engineering vectors. Attackers could exploit the open redirect to craft convincing phishing campaigns that redirect users to malicious sites, potentially leading to credential compromise or malware infections. This risk is heightened in sectors where secure communication is critical, such as government, finance, healthcare, and critical infrastructure. Although the vulnerability requires user interaction, the widespread use of Nextcloud in privacy-conscious environments means that successful exploitation could erode trust in internal communication tools and lead to data breaches or unauthorized access. The impact on confidentiality is indirect but significant if attackers leverage the redirect to harvest credentials or deliver payloads. Integrity and availability impacts are minimal as the vulnerability does not allow direct code execution or denial of service. The lack of known exploits in the wild suggests limited active targeting, but the potential for phishing campaigns remains a concern. Organizations relying on Nextcloud Talk for secure messaging should consider this vulnerability a medium risk that could facilitate targeted attacks against their users.

1. Immediate upgrade of all Nextcloud Talk Android clients to version 12.1.2 or later to ensure the vulnerability is patched. 2. Implement user awareness training focused on recognizing suspicious links and the risks of clicking on unexpected geolocation previews or links within messaging apps. 3. Deploy mobile device management (MDM) solutions to enforce app updates and restrict installation of outdated or vulnerable app versions. 4. Monitor network traffic and logs for unusual redirect patterns or connections to untrusted domains originating from Nextcloud Talk clients. 5. Integrate URL filtering and web gateway solutions to block access to known malicious domains that could be used in phishing campaigns exploiting this vulnerability. 6. Encourage the use of multi-factor authentication (MFA) on Nextcloud accounts to reduce the impact of credential theft resulting from phishing. 7. Coordinate with Nextcloud administrators to audit and restrict external link sharing policies within the organization to minimize exposure to malicious redirects. These measures go beyond generic patching by combining technical controls with user education and monitoring to reduce the likelihood and impact of exploitation.