CVE-2021-43558 : Security Advisory and Response

A flaw was found in Moodle in versions 3.11 to 3.11.3, 3.10 to 3.10.7, 3.9 to 3.9.10, and earlier unsupported versions, posing a reflected XSS risk through a URL parameter in the filetype site administrator tool that needed additional sanitizing.

Understanding CVE-2021-43558

This CVE relates to a security vulnerability in Moodle versions 3.9.11, 3.10.8, and 3.11.4 as well as earlier unsupported versions.

What is CVE-2021-43558?

The CVE-2021-43558 vulnerability affects Moodle, an open-source learning platform. It centers around insufficient sanitizing of a URL parameter in the site administrator tool, leading to a reflected XSS risk.

The Impact of CVE-2021-43558

Malicious actors could exploit this vulnerability to execute arbitrary scripts in a user's browser, potentially compromising sensitive information.
Successful exploitation could result in unauthorized access, data theft, and further attacks on the Moodle platform.

Technical Details of CVE-2021-43558

This section delves into the specifics of the vulnerability.

Vulnerability Description

The flaw in Moodle versions 3.9 to 3.11.3 and earlier unsupported versions stemmed from insufficient sanitization of a specific URL parameter in the admin tool.

Affected Systems and Versions

Affected Versions: Moodle 3.9.11, 3.10.8, 3.11.4, and prior unsupported versions
Systems: Moodle instances running the mentioned versions are susceptible to the XSS risk.

Exploitation Mechanism

Malicious actors can exploit the vulnerability by crafting a specific URL to inject and execute malicious scripts, leading to a reflected XSS attack.

Mitigation and Prevention

It's crucial to take immediate steps to mitigate the CVE-2021-43558 vulnerability and enhance the overall security posture of Moodle.

Immediate Steps to Take

Update Moodle to the latest patched version promptly to address the XSS risk.
Inform users to be cautious of clicking on suspicious links within Moodle.
Consider implementing a web application firewall (WAF) to detect and mitigate XSS attacks.

Long-Term Security Practices

Regularly monitor Moodle security advisories and update procedures to stay informed about future vulnerabilities.
Conduct security assessments and penetration testing to proactively identify and address potential security gaps.
Educate Moodle administrators and users on cybersecurity best practices to prevent successful attacks.
Implement content security policies (CSP) to control resource loading and mitigate XSS risks.

Patching and Updates

Stay informed about security updates released by Moodle for addressing vulnerabilities like CVE-2021-43558.
Prioritize timely installation of patches and updates to prevent exploitation of known security flaws.