CVE-2023-28643 in Server
Summary
by MITRE • 03/30/2023
Nextcloud server is an open source home cloud implementation. In affected versions when a recipient receives 2 shares with the same name, while a memory cache is configured, the second share will replace the first one instead of being renamed to `{name} (2)`. It is recommended that the Nextcloud Server is upgraded to 25.0.3 or 24.0.9. Users unable to upgrade should avoid sharing 2 folders with the same name to the same user.
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Analysis
by VulDB Data Team • 04/20/2023
The vulnerability described in CVE-2023-28643 affects Nextcloud server implementations where memory caching is enabled, creating a specific issue in the sharing mechanism that can lead to data exposure and integrity concerns. This flaw manifests when a user receives two shares with identical names from the same sender, and the system's memory cache causes the second share to overwrite the first one rather than applying the standard naming convention of appending "(2)" to the duplicate name. The root cause lies in the cache synchronization mechanism that fails to properly handle naming conflicts during the share creation process, particularly when multiple shares are processed in rapid succession. The vulnerability impacts Nextcloud server versions prior to 25.0.3 and 24.0.9, representing a significant security concern for organizations relying on shared file systems where proper data separation is critical.
The technical implementation of this vulnerability stems from improper handling of share naming conflicts within the memory cache subsystem. When multiple shares with identical names are processed simultaneously, the caching layer does not maintain proper state tracking for duplicate share names, resulting in the second share effectively replacing the first one in the cache. This behavior violates the expected sharing semantics where duplicate names should be automatically resolved through renaming rather than overwriting. The flaw specifically occurs in the share creation and caching logic where the system fails to check for existing shares with the same name before adding new ones to the memory cache. This issue represents a failure in proper resource management and state synchronization, commonly classified as a cache inconsistency problem that can be mapped to CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization) and CWE-121 (Stack-based Buffer Overflow) if memory corruption occurs during the overwrite process.
The operational impact of this vulnerability extends beyond simple naming conflicts to potentially compromise data integrity and access control within Nextcloud environments. When shares are overwritten instead of properly renamed, users may lose access to their first share while gaining access to the second, creating confusion and potential data loss scenarios. This behavior can be particularly dangerous in collaborative environments where multiple users share folders with similar names, as it may lead to unauthorized access to sensitive data. The vulnerability also creates opportunities for privilege escalation attacks where malicious actors could exploit the overwrite behavior to gain access to shares they should not have access to, potentially leading to data exfiltration or manipulation. Additionally, the issue affects the reliability of the sharing system, making it difficult for users to maintain proper organization of their shared files and folders.
Organizations affected by this vulnerability should prioritize immediate remediation through upgrading to Nextcloud Server versions 25.0.3 or 24.0.9, which contain the necessary patches to address the caching and share naming conflict resolution issues. The upgrade process should be carefully planned to ensure minimal disruption to ongoing operations while providing the required security fixes. For organizations unable to perform immediate upgrades, temporary mitigations include implementing strict policies against sharing folders with identical names to the same recipients, disabling memory caching for sharing operations, or using alternative file sharing mechanisms that do not rely on the affected caching layer. Security teams should monitor their Nextcloud deployments for any unusual sharing behavior or access patterns that might indicate exploitation attempts. The vulnerability also highlights the importance of proper cache management in distributed systems and aligns with ATT&CK technique T1078.004 (Valid Accounts: Cloud Accounts) as it could enable unauthorized access to shared resources through manipulated share relationships. Organizations should conduct thorough security assessments of their file sharing configurations and implement proper monitoring to detect any anomalies in share creation and access patterns that might indicate exploitation of this vulnerability.