CVE-2022-36075 in Files Access Control
Summary
by MITRE • 09/16/2022
Nextcloud files access control is a nextcloud app to manage access control for files. Users with limited access can see file names in certain cases where they do not have privilege to do so. This issue has been addressed and it is recommended that the Nextcloud Files Access Control app is upgraded to 1.12.2, 1.13.1 or 1.14.1. There are no known workarounds for this issue
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Analysis
by VulDB Data Team • 10/18/2022
The vulnerability described in CVE-2022-36075 affects the Nextcloud Files Access Control application, which is designed to manage and enforce access control policies for files within the Nextcloud platform. This particular flaw represents a critical authorization bypass issue that undermines the fundamental security model of the system. The vulnerability specifically impacts users who have been granted limited access privileges to certain files or directories, creating an unintended information disclosure scenario where these restricted users can potentially discover file names that they should not be able to access. This represents a significant deviation from the expected security boundaries and could enable malicious actors or unauthorized users to gain insights into the file structure and content organization of systems they should not have visibility into.
The technical implementation flaw within the Nextcloud Files Access Control app stems from inadequate validation of access permissions during file listing and enumeration operations. When users with restricted privileges attempt to browse directories or access file metadata, the application fails to properly enforce the access control policies that should prevent them from seeing file names in certain contexts. This issue manifests in cases where the system should be restricting visibility to specific files but instead allows the display of filenames, effectively leaking information about the existence and structure of files that should remain hidden from unauthorized users. The vulnerability is particularly concerning because it operates at the application level rather than the network or system level, making it more subtle and harder to detect through traditional network monitoring approaches.
The operational impact of this vulnerability extends beyond simple information disclosure to potentially enable more sophisticated attacks. An attacker who can enumerate file names in restricted directories may be able to identify sensitive files, understand organizational data structures, or even map out the overall file hierarchy of a Nextcloud instance. This information can then be leveraged for further attacks such as targeted phishing attempts, social engineering campaigns, or more advanced exploitation techniques that rely on knowledge of file names and system organization. The vulnerability also undermines the principle of least privilege that is fundamental to secure system design, as it allows users to access information that should be restricted based on their assigned permissions. According to CWE-284, this represents an improper access control issue where the application fails to properly enforce access restrictions, and aligns with ATT&CK technique T1213.002 for data from information repositories where unauthorized access to file listings can be achieved.
Organizations using Nextcloud with the affected Files Access Control app should immediately upgrade to version 1.12.2, 1.13.1, or 1.14.1 to remediate this vulnerability. The absence of known workarounds means that organizations cannot implement temporary mitigations while waiting for the official patch. This vulnerability highlights the importance of proper access control implementation and the need for thorough testing of permission systems, particularly in applications that handle sensitive data. The patch addresses the underlying logic error in how the application validates access permissions during file enumeration operations, ensuring that users cannot see file names when they lack appropriate privileges. Security teams should also conduct comprehensive audits of their Nextcloud installations to verify that no other similar access control issues exist within their environment, particularly in custom applications or third-party plugins that may interact with the core file access system. The vulnerability serves as a reminder of the critical importance of maintaining up-to-date software and the potential consequences of outdated applications that may contain known security flaws.