CVE-2021-27131 Explained : Impact and Mitigation

Moodle 3.10.1 is found to be vulnerable to persistent/stored cross-site scripting (XSS) due to improper input sanitization in the "Additional HTML Section" via the "Header and Footer" parameter in /admin/settings.php. This vulnerability allows an attacker to steal admin and user account cookies by storing malicious XSS payloads in the Header and Footer section. Please note that this vulnerability is disputed by the vendor as the unsanitized input is intentionally allowed for administrators

Understanding CVE-2021-27131

This section provides insights into the impact, technical details, and mitigation strategies for CVE-2021-27131.

What is CVE-2021-27131?

CVE-2021-27131 is a persistent cross-site scripting vulnerability affecting Moodle 3.10.1. It arises due to inadequate input sanitization in the "Additional HTML Section" under the "Header and Footer" parameter.

The Impact of CVE-2021-27131

The vulnerability could be exploited by attackers to inject malicious scripts into the Moodle platform, potentially compromising the security and privacy of admin and user accounts.

Technical Details of CVE-2021-27131

Let's explore the vulnerability description, affected systems, and exploitation mechanism in this section.

Vulnerability Description

The XSS vulnerability in Moodle 3.10.1 enables threat actors to execute unauthorized scripts by inserting malicious code into the Header and Footer section, leading to unauthorized data access.

Affected Systems and Versions

All instances of Moodle version 3.10.1 are impacted by CVE-2021-27131, exposing them to the risk of cross-site scripting attacks via the "Additional HTML Section.".

Exploitation Mechanism

By leveraging the lack of input sanitization in the Header and Footer parameter, attackers can implant XSS payloads to extract sensitive data like admin and user cookies.

Mitigation and Prevention

Discover the crucial steps to take immediately, along with long-term security practices and the significance of timely patching and updates.

Immediate Steps to Take

Administrators should restrict access to the "Additional HTML Section" feature, allowing only trusted users to input unsanitized data.
Regularly monitor Moodle for any suspicious activities or unauthorized changes to the Header and Footer sections.

Long-Term Security Practices

Educate administrators on the risks associated with unsanitized input and provide training on secure coding practices.
Implement automated scanning tools to identify and mitigate XSS vulnerabilities across the Moodle platform.

Patching and Updates

Ensure the timely application of security patches released by Moodle to address the XSS vulnerability in version 3.10.1.