CVE-2020-8153 in Groupfolders App
Summary
by MITRE
Improper access control in Groupfolders app 4.0.3 allowed to delete hidden directories when when renaming an accessible item to the same name.
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Analysis
by VulDB Data Team • 05/13/2020
The vulnerability identified as CVE-2020-8153 represents a critical access control flaw within the Groupfolders application version 4.0.3, specifically affecting Nextcloud deployments that utilize this module for collaborative file management. This weakness stems from insufficient validation mechanisms during directory renaming operations, creating a scenario where unauthorized deletion of hidden directories becomes possible through seemingly benign user actions. The vulnerability manifests when a user with appropriate permissions attempts to rename a directory to its existing name, inadvertently triggering a condition that allows the system to remove hidden subdirectories within the target folder structure.
The technical root cause of this vulnerability lies in the improper implementation of access control checks during file system operations, particularly during rename operations that should maintain consistent permission boundaries. When a user performs a rename action that effectively results in no change to the directory name, the application fails to properly validate whether the operation should be restricted based on the user's access level to the target directory structure. This flaw creates a privilege escalation pathway where users can exploit the system's inconsistent handling of hidden files and directories to delete content they should not have access to.
From an operational perspective, this vulnerability poses significant risks to organizations relying on Nextcloud Groupfolders for collaborative environments, as it enables malicious users to remove sensitive data without proper authorization. The impact extends beyond simple data loss, as the vulnerability can be leveraged to disrupt workflows, compromise data integrity, and potentially expose confidential information stored within hidden directories that are typically protected from casual access. Attackers could exploit this weakness to systematically remove important files or directories that contain sensitive organizational data, particularly in environments where hidden directories are used for temporary storage or configuration files.
The vulnerability aligns with CWE-284, which addresses improper access control issues in software applications, and can be mapped to ATT&CK technique T1078.004 for valid accounts and T1486 for data encryption for ransom. Organizations implementing Nextcloud Groupfolders should immediately apply the vendor-provided patch that addresses this access control weakness by implementing proper validation checks during rename operations and ensuring that all file system modifications respect existing permission boundaries. Additionally, administrators should review user access permissions and implement monitoring solutions to detect anomalous directory deletion patterns that could indicate exploitation attempts. The recommended mitigation strategy includes not only applying the security patch but also conducting comprehensive access control reviews and implementing network segmentation to limit potential lateral movement if exploitation occurs.