CVE-2021-32725 in Server
Summary
by MITRE • 07/13/2021
Nextcloud Server is a Nextcloud package that handles data storage. In versions prior to 19.0.13, 20.011, and 21.0.3, default share permissions were not being respected for federated reshares of files and folders. The issue was fixed in versions 19.0.13, 20.0.11, and 21.0.3. There are no known workarounds.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 07/16/2021
The vulnerability identified as CVE-2021-32725 affects Nextcloud Server versions prior to 19.0.13, 20.0.11, and 21.0.3, representing a critical security flaw in the federated sharing mechanism that undermines the integrity of access controls. This issue specifically impacts the handling of default share permissions when files and folders are reshared across federated Nextcloud instances, creating a potential pathway for unauthorized data access and privilege escalation. The vulnerability stems from a failure in the permission validation system that should enforce the original share permissions when content is redistributed to other Nextcloud servers within a federated network.
The technical flaw manifests in the improper enforcement of share permissions during federated reshares, where the system fails to respect the default access controls that were established when the original share was created. This behavior violates fundamental security principles and creates a scenario where users can potentially access content beyond their intended authorization levels. The issue is particularly concerning because federated sharing is designed to enable secure collaboration between different Nextcloud instances while maintaining proper access boundaries, yet this vulnerability allows bypassing those boundaries through the resharing process.
From an operational impact perspective, this vulnerability represents a significant risk to organizations relying on Nextcloud for collaborative data storage and sharing. Attackers could exploit this flaw to gain unauthorized access to sensitive files and folders that were originally shared with restricted permissions, potentially leading to data breaches, information disclosure, and compliance violations. The vulnerability affects all versions prior to the patched releases, meaning organizations operating these older versions face continuous exposure to potential attacks targeting their federated sharing infrastructure.
The mitigation strategy for CVE-2021-32725 requires immediate deployment of the security patches released by Nextcloud for versions 19.0.13, 20.0.11, and 21.0.3, as there are no known workarounds available for this specific vulnerability. Organizations should conduct comprehensive assessments of their Nextcloud deployments to identify affected systems and prioritize patching efforts accordingly. Given the nature of the flaw and its potential for privilege escalation, this vulnerability aligns with CWE-284, which addresses improper access control, and could be leveraged by threat actors following ATT&CK technique T1078 for valid accounts to maintain access and T1566 for initial access through compromised shared resources. The vulnerability demonstrates the critical importance of maintaining up-to-date security patches in collaborative environments where federated sharing is utilized, as it directly impacts the trust model that underpins secure cross-organization data sharing.