CVE-2021-41177 : Vulnerability Insights and Analysis

Nextcloud Server versions < 20.0.13, >= 21.0.0, < 21.0.5, and < 22.2.0 are affected by a vulnerability where rate-limits don't work without a memory cache backend configured.

Understanding CVE-2021-41177

What is CVE-2021-41177?

Nextcloud, an open-source, self-hosted productivity platform, suffers from a flaw where rate-limiting does not function correctly on servers lacking a memory cache backend.

The Impact of CVE-2021-41177

The vulnerability has a CVSS base score of 8.1 (High severity) with a high impact on availability and confidentiality. It requires low privileges to exploit over the network.

Technical Details of CVE-2021-41177

Vulnerability Description

The issue is due to Nextcloud Server not implementing a database backend for rate-limiting, causing rate-limits to be ineffective without a memory cache backend.

Affected Systems and Versions

Nextcloud Server < 20.0.13
Nextcloud Server >= 21.0.0, < 21.0.5
Nextcloud Server < 22.2.0

Exploitation Mechanism

The vulnerability can be exploited by an attacker with network access and low privileges to impact availability and expose confidential information.

Mitigation and Prevention

Immediate Steps to Take

Upgrade Nextcloud Server to versions 20.0.13, 21.0.5, or 22.2.0
Enable a memory cache backend in

config.php

Long-Term Security Practices

Regularly update Nextcloud Server to the latest version
Implement additional security measures to protect against similar vulnerabilities

Patching and Updates

Apply patches provided by Nextcloud to address the rate-limiting issue.