CVE-2023-48239 in Server
Summary
by MITRE • 11/21/2023
Nextcloud Server provides data storage for Nextcloud, an open source cloud platform. Starting in version 25.0.0 and prior to versions 25.0.13, 26.0.8, and 27.1.3 of Nextcloud Server and starting in version 20.0.0 and prior to versions 20.0.14.16, 21.0.9.13, 22.2.10.15, 23.0.12.12, 24.0.12.8, 25.0.13, 26.0.8, and 27.1.3 of Nextcloud Enterprise Server, a malicious user could update any personal or global external storage, making them inaccessible for everyone else as well. Nextcloud Server 25.0.13, 26.0.8, and 27.1.3 and Nextcloud Enterprise Server is upgraded to 20.0.14.16, 21.0.9.13, 22.2.10.15, 23.0.12.12, 24.0.12.8, 25.0.13, 26.0.8, and 27.1.3 contain a patch for this issue. As a workaround, disable app files_external. This workaround also makes the external storage inaccessible but retains the configurations until a patched version has been deployed.
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Analysis
by VulDB Data Team • 12/15/2023
This vulnerability affects Nextcloud Server and Nextcloud Enterprise Server implementations where a malicious user can manipulate external storage configurations to render them inaccessible to other users. The issue exists in versions starting from 25.0.0 through 25.0.12, 26.0.0 through 26.0.7, and 27.0.0 through 27.1.2 for the community edition, alongside corresponding enterprise versions up to 20.0.14.15, 21.0.9.12, 22.2.10.14, 23.0.12.11, 24.0.12.7, 25.0.12, 26.0.7, and 27.1.2. The vulnerability stems from insufficient access controls and validation mechanisms within the external storage management functionality, allowing unauthorized modification of storage configurations.
The technical flaw manifests through a privilege escalation vulnerability where an authenticated malicious user can exploit the external storage update mechanism to modify both personal and global external storage configurations. This flaw enables attackers to manipulate storage mount points, credentials, or access parameters in a way that makes the affected storage inaccessible to legitimate users. The vulnerability is particularly concerning because it affects both individual user configurations and system-wide settings, potentially causing widespread disruption to data access across the platform. This type of vulnerability maps to CWE-284 Access Control Issues, specifically related to insufficient access control for external storage management functions.
The operational impact of this vulnerability is significant as it can lead to complete data unavailability for legitimate users while maintaining the attacker's access to the compromised storage resources. Organizations relying on Nextcloud for collaborative data storage and file sharing face potential business disruption when external storage becomes inaccessible due to malicious configuration changes. The vulnerability affects not only individual users but also system administrators who may lose access to critical data repositories. This scenario represents a classic case of privilege abuse that can result in denial of service conditions and data integrity compromise. From an adversarial perspective, this vulnerability aligns with ATT&CK technique T1078 Valid Accounts, where attackers leverage legitimate user credentials to perform unauthorized modifications that affect system availability.
Security mitigations for this vulnerability include upgrading to patched versions of Nextcloud Server and Nextcloud Enterprise Server, specifically versions 25.0.13, 26.0.8, and 27.1.3 for community editions, and their corresponding enterprise versions. The recommended workaround of disabling the files_external app provides temporary relief by preventing further external storage modifications, though it also makes all external storage inaccessible until a proper patch is applied. System administrators should implement monitoring for unauthorized external storage configuration changes and consider additional access controls for storage management functions. The patch addresses the core access control issue by implementing proper validation and authorization checks for external storage update operations, ensuring that only authorized users can modify storage configurations. Organizations should also conduct thorough security assessments of their Nextcloud implementations to identify any potential exploitation attempts and ensure proper network segmentation to limit the attack surface.