CVE-2021-22895 in Desktop Client
Summary
by MITRE • 06/11/2021
Nextcloud Desktop Client before 3.3.1 is vulnerable to improper certificate validation due to lack of SSL certificate verification when using the "Register with a Provider" flow.
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Analysis
by VulDB Data Team • 06/14/2021
The vulnerability identified as CVE-2021-22895 affects the Nextcloud Desktop Client version 3.3.0 and earlier, presenting a critical security flaw in the certificate validation process during the registration workflow. This issue stems from the client's failure to properly verify SSL certificates when users attempt to register their accounts through the "Register with a Provider" functionality. The improper certificate validation creates a significant attack surface that could allow malicious actors to intercept and manipulate communications between the desktop client and Nextcloud servers.
The technical root cause of this vulnerability lies in the client's implementation of secure communication protocols where SSL certificate verification is either disabled or bypassed during the registration process. This flaw falls under the category of weak cryptographic practices and improper certificate validation as defined by CWE-295, which specifically addresses issues related to certificate validation and trust management. When the client fails to validate SSL certificates, it becomes susceptible to man-in-the-middle attacks where attackers can present fake certificates to establish fraudulent connections with users.
The operational impact of this vulnerability extends beyond simple data interception, as it fundamentally undermines the security model of the Nextcloud desktop client. Attackers could exploit this weakness to perform session hijacking, steal authentication credentials, or inject malicious content into the communication channel between users and Nextcloud servers. The vulnerability is particularly dangerous because it occurs during the initial registration process, which is when users are most likely to be establishing trust relationships with the service. This creates a window of opportunity for attackers to compromise user accounts and gain unauthorized access to sensitive data stored in Nextcloud environments.
Organizations relying on Nextcloud Desktop Client for file synchronization and collaboration face significant risks when this vulnerability remains unaddressed. The lack of proper certificate validation means that even if users believe they are connecting to legitimate Nextcloud servers, they could be communicating with malicious intermediaries. This vulnerability directly relates to ATT&CK technique T1046 which involves network service scanning, and T1566 which covers credential access through social engineering or network infiltration. The attack surface is further expanded by the fact that this vulnerability affects both personal and enterprise deployments, making it a widespread concern across various organizational environments.
The recommended mitigation strategy involves immediate deployment of Nextcloud Desktop Client version 3.3.1 or later, which includes the necessary fixes to restore proper SSL certificate validation. Organizations should also implement additional monitoring to detect anomalous certificate behavior or unexpected connection patterns. Security teams should review their existing certificate management policies and ensure that all client-side applications maintain proper TLS validation. The vulnerability demonstrates the critical importance of maintaining up-to-date security practices and highlights the necessity of comprehensive testing of secure communication channels, particularly during user onboarding processes. Additionally, network administrators should consider implementing certificate pinning mechanisms as an additional layer of protection against certificate-based attacks, ensuring that the client only accepts specific trusted certificates from known Nextcloud servers.