CVE-2023-39958 : Security Advisory and Response

A vulnerability has been discovered in Nextcloud Server that leads to missing brute force protection on password reset token OAuth2 API controller.

Understanding CVE-2023-39958

This vulnerability, identified as CWE-307: Improper Restriction of Excessive Authentication Attempts, affects Nextcloud Server versions prior to 22.2.10.13, 23.0.12.8, 24.0.12.5, 25.0.9, 26.0.4, and 27.0.1, allowing attackers to brute force client secrets of OAuth2 clients.

What is CVE-2023-39958?

Nextcloud Server, an open-source cloud platform for data storage, is impacted by missing protection, enabling potential brute force attacks on client secrets.

The Impact of CVE-2023-39958

This vulnerability could result in unauthorized access to sensitive information, compromising the security and confidentiality of data stored on affected Nextcloud Server versions.

Technical Details of CVE-2023-39958

The following provides more information regarding the vulnerability:

Vulnerability Description

The missing protection exposes Nextcloud Server instances to brute force attacks on OAuth2 client secrets.

Affected Systems and Versions

Versions >= 22.0.0, < 22.2.10.13
Versions >= 23.0.0, < 23.0.12.8
Versions >= 24.0.0, < 24.0.12.5
Versions >= 25.0.0, < 25.0.9
Versions >= 26.0.0, < 26.0.4
Versions >= 27.0.0, < 27.0.1

Exploitation Mechanism

Attackers can exploit this vulnerability by attempting multiple authentication requests to discover client secrets through brute force attacks.

Mitigation and Prevention

To address CVE-2023-39958, consider the following steps:

Immediate Steps to Take

Update Nextcloud Server to the patched versions mentioned above.
Implement additional security measures to protect against brute force attacks.

Long-Term Security Practices

Regularly monitor and update security configurations on the server.
Educate users on best practices for password security and OAuth2 client secret management.

Patching and Updates

Apply available patches and security updates promptly to safeguard Nextcloud Server from known vulnerabilities.