CVE-2021-41239 : Exploit Details and Defense Strategies

Nextcloud server allows user enumeration in certain versions, potentially exposing sensitive information to unauthorized actors.

Understanding CVE-2021-41239

Nextcloud server vulnerability disregards user enumeration settings, leading to potential sensitive information exposure.

What is CVE-2021-41239?

In affected versions of Nextcloud server, the User Status API fails to consider user enumeration settings by administrators, allowing users to list other users even when disabled, posing a privacy risk.

The Impact of CVE-2021-41239

The vulnerability could lead to unauthorized users enumerating users on the instance, potentially exposing sensitive information, despite user listing restrictions.

Technical Details of CVE-2021-41239

This section covers the technical aspects and implications of the CVE.

Vulnerability Description

Nextcloud server versions <= 20.0.14, >= 21.0.0 and < 21.0.6, >= 22.2.0 and < 22.2.1 are affected.

Affected Systems and Versions

Versions affected: <= 20.0.14, >= 21.0.0 and < 21.0.6, >= 22.2.0 and < 22.2.1

Exploitation Mechanism

Attack Complexity: Low
Attack Vector: Network
Base Score: 5.3 (Medium)

Mitigation and Prevention

Protecting systems from CVE-2021-41239 requires immediate actions and long-term security measures.

Immediate Steps to Take

Upgrade Nextcloud server to versions 20.0.14, 21.0.6, or 22.2.1 to mitigate the vulnerability.

Long-Term Security Practices

Regularly review and update access control and user enumeration settings.
Monitor and restrict user access and privileges to sensitive information.

Patching and Updates

Stay informed about security updates and patches released by Nextcloud to address vulnerabilities.