CVE-2021-44856 Explained : Impact and Mitigation

An issue was discovered in MediaWiki before 1.35.5, 1.36.x before 1.36.3, and 1.37.x before 1.37.1. A title blocked by AbuseFilter can be created via Special:ChangeContentModel due to the mishandling of the EditFilterMergedContent hook return value.

Understanding CVE-2021-44856

What is CVE-2021-44856?

CVE-2021-44856 is a vulnerability found in MediaWiki versions before 1.35.5, 1.36.x before 1.36.3, and 1.37.x before 1.37.1. It allows the creation of a blocked title via Special:ChangeContentModel due to mishandling of a specific hook return value.

The Impact of CVE-2021-44856

This vulnerability could potentially be exploited by malicious users to bypass security measures and create titles that are supposed to be blocked, potentially leading to unauthorized content creation or manipulation.

Technical Details of CVE-2021-44856

Vulnerability Description

The issue arises from the mishandling of the EditFilterMergedContent hook return value, enabling the creation of blocked titles through Special:ChangeContentModel.

Affected Systems and Versions

MediaWiki versions before 1.35.5
MediaWiki versions 1.36.x before 1.36.3
MediaWiki versions 1.37.x before 1.37.1

Exploitation Mechanism

Attackers can exploit this vulnerability by leveraging the mishandling of the hook return value to circumvent title blocking by AbuseFilter.

Mitigation and Prevention

Immediate Steps to Take

Update MediaWiki to version 1.35.5, 1.36.3, or 1.37.1, which contain fixes for this vulnerability.
Monitor for any unauthorized title creations on MediaWiki instances.

Long-Term Security Practices

Regularly update software and apply security patches to prevent known vulnerabilities.
Implement access controls and monitoring to detect unauthorized activities.

Patching and Updates

Ensure timely application of security updates and patches provided by MediaWiki to address this vulnerability.