CVE-2016-9462 in ownCloud Server
Summary
by MITRE
Nextcloud Server before 9.0.52 & ownCloud Server before 9.0.4 are not properly verifying restore privileges when restoring a file. The restore capability of Nextcloud/ownCloud was not verifying whether a user has only read-only access to a share. Thus a user with read-only access was able to restore old versions.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 11/22/2022
The vulnerability identified as CVE-2016-9462 represents a critical access control flaw in Nextcloud and ownCloud server implementations that affects versions prior to 9.0.52 and 9.0.4 respectively. This issue stems from insufficient privilege verification during the file restoration process, creating a scenario where users with limited read-only access can bypass intended restrictions and perform operations that should be restricted to users with higher permissions. The flaw specifically impacts the restore functionality of shared files, where the system fails to properly validate whether a user possesses the necessary write permissions before allowing restoration of previous file versions. This vulnerability directly violates the principle of least privilege and demonstrates a failure in the authorization mechanism that governs file access operations within the cloud storage platform.
The technical implementation of this vulnerability occurs at the application level where the restore functionality does not properly enforce access control checks before executing file restoration operations. When a user attempts to restore a file version, the system should verify that the user has write permissions to the target file or directory. However, the flawed implementation allows read-only share participants to successfully restore previous versions of files, effectively granting them write privileges that they should not possess. This represents a classic authorization bypass vulnerability that can be categorized under CWE-284 which specifically addresses improper access control. The flaw exists in the core file management logic where the system assumes that users who can access a file through a share can also restore it, without properly validating the permission level of the sharing relationship.
The operational impact of this vulnerability is significant for organizations relying on Nextcloud or ownCloud for collaborative file sharing and document management. A malicious or unauthorized user with read-only access to shared files could potentially overwrite current file versions with older content, leading to data corruption, information loss, or the introduction of outdated information into shared workspaces. This capability undermines the integrity of shared documents and can result in compliance violations where organizations must maintain proper access controls and audit trails. The vulnerability also creates a risk for business continuity as users with read-only access could inadvertently or deliberately restore files to previous states, potentially reverting important changes or introducing security vulnerabilities from older versions of documents. Organizations may face audit failures or regulatory penalties if they cannot demonstrate proper access controls over shared content.
Mitigation strategies for CVE-2016-9462 require immediate implementation of software updates to versions 9.0.52 or later for Nextcloud and 9.0.4 or later for ownCloud, which contain the necessary fixes to properly validate restore privileges. System administrators should also implement additional monitoring and logging of file restoration activities to detect unauthorized access attempts. Organizations should conduct comprehensive access control reviews to ensure that sharing permissions are properly configured and that read-only shares do not inadvertently grant restoration capabilities. The fix addresses the underlying authorization logic by implementing proper permission checks before allowing restore operations, aligning with the ATT&CK framework's privilege escalation techniques where unauthorized users attempt to gain elevated access through legitimate system functions. Additionally, organizations should consider implementing network-level controls and access restrictions to limit exposure while patches are deployed, ensuring that only authorized personnel can access sensitive shared resources.