CVE-2021-32658 in Nextcloud
Summary
by MITRE • 06/09/2021
Nextcloud Android is the Android client for the Nextcloud open source home cloud system. Due to a timeout issue the Android client may not properly clean all sensitive data on account removal. This could include sensitive key material such as the End-to-End encryption keys. It is recommended that the Nextcloud Android App is upgraded to 3.16.1
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 06/11/2021
The vulnerability identified as CVE-2021-32658 affects the Nextcloud Android client application, which serves as the mobile interface for the Nextcloud open source home cloud system. This security flaw stems from an improper handling of data cleanup procedures during account removal processes. The Nextcloud platform is widely deployed for personal and enterprise file synchronization and sharing, making its mobile client a critical component of user data protection. The vulnerability specifically impacts the Android version of the client application, which is used by millions of users worldwide for accessing their cloud storage and collaborative workspaces.
The technical root cause of this vulnerability lies in a timeout issue that prevents the Android client from properly executing all required data cleanup operations when a user removes their account from the application. During the account removal process, the application should systematically purge all sensitive information including encryption keys, authentication tokens, and cached data. However, due to the timeout condition, certain cleanup operations may be interrupted or skipped, leaving residual sensitive data on the device. This flaw is particularly concerning because it directly affects the end-to-end encryption implementation that Nextcloud employs to protect user data. The encryption keys, which are essential for decrypting files stored on the cloud, may remain accessible on the local device even after account removal, creating a potential security risk.
The operational impact of this vulnerability extends beyond simple data retention concerns and represents a significant threat to user privacy and data security. When users remove their Nextcloud accounts from the Android application, they expect all associated sensitive information to be completely purged from their device. However, the persistence of encryption keys and other sensitive materials means that unauthorized parties who gain access to the device could potentially reconstruct the encryption keys and access previously encrypted files stored in the cloud. This vulnerability aligns with CWE-200, which addresses information exposure, and CWE-312, which covers cleartext storage of sensitive information. The implications are particularly severe for users who store highly confidential data in their Nextcloud accounts, as the compromised encryption keys could enable decryption of sensitive documents, photos, and other personal information.
The remediation for this vulnerability requires immediate upgrading of the Nextcloud Android application to version 3.16.1 or later, as recommended by the vendor. This update addresses the timeout issue that was preventing proper data cleanup operations during account removal. Security practitioners should prioritize this patch deployment across all affected devices, particularly in enterprise environments where Nextcloud is extensively used for collaborative work and data sharing. The vulnerability demonstrates the critical importance of proper resource management and timeout handling in mobile applications, especially those dealing with sensitive cryptographic data. Organizations should also implement monitoring procedures to detect any unauthorized access attempts to devices that may have been affected by this vulnerability before the patch was applied, as outlined in the mitre ATT&CK framework under techniques related to credential access and data exfiltration.
This vulnerability highlights the broader challenge of secure data deletion in mobile applications, where network timeouts and asynchronous operations can lead to incomplete cleanup procedures. The Nextcloud Android client's handling of encryption keys during account removal represents a failure in proper secure deletion practices that should be implemented across all mobile security applications. The flaw underscores the need for comprehensive testing of edge cases in mobile applications, particularly around resource constraints and network conditions that may affect critical security operations. Security teams should conduct thorough assessments of other mobile applications that handle similar cryptographic materials to identify potential vulnerabilities in their own environments, ensuring that proper timeout handling and secure deletion protocols are implemented consistently across all platforms and applications that process sensitive user data.