CVE-2021-41241 Explained : Impact and Mitigation

Nextcloud server is a self-hosted system designed to provide cloud-style services. The vulnerability in the groupfolders application allows unauthorized access to subfolders.

Understanding CVE-2021-41241

The security flaw in Nextcloud's groupfolders application permits access to subfolders despite advanced permissions settings.

What is CVE-2021-41241?

The groupfolders feature in Nextcloud fails to enforce advanced permissions properly, enabling users to access subfolders they should not be able to.

The Impact of CVE-2021-41241

The vulnerability poses a medium severity threat with a CVSS base score of 4.3, allowing for unauthorized access to confidential data within the subfolders.

Technical Details of CVE-2021-41241

The vulnerability affects Nextcloud's groupfolders application, leading to unauthorized access to subfolders.

Vulnerability Description

Due to an authorization check failure, users can bypass access restrictions and view subfolders within groupfolders.

Affected Systems and Versions

Nextcloud versions < 20.0.14
Nextcloud versions >= 21.0.0, < 21.0.6
Nextcloud versions >= 22.2.0, < 22.2.1

Exploitation Mechanism

By copying the groupfolder to another location, a user can circumvent the permission checks and gain access to subfolders.

Mitigation and Prevention

Take immediate action to prevent unauthorized access and secure your Nextcloud server.

Immediate Steps to Take

Upgrade Nextcloud Server to versions 20.0.14, 21.0.6, or 22.2.1
Disable the groupfolders application in the admin settings if upgrading is not feasible

Long-Term Security Practices

Regularly update Nextcloud to the latest version
Monitor security advisories from Nextcloud for any new vulnerabilities

Patching and Updates

Apply patches provided by Nextcloud promptly to address security vulnerabilities.