CVE-2020-25627: Moodle Stored XSS Vulnerability

CVE-2020-25627 Overview

CVE-2020-25627 is a stored Cross-Site Scripting (XSS) vulnerability affecting the Moodle learning management system. The moodlenetprofile user profile field lacked proper sanitization, allowing attackers to inject and store malicious JavaScript code that would execute in the browsers of other users viewing the affected profile.

Critical Impact

Attackers can inject persistent malicious scripts into user profile fields, potentially compromising user sessions, stealing credentials, or performing actions on behalf of authenticated users within the Moodle platform.

Affected Products

• Moodle version 3.9
• Moodle version 3.9.1

Discovery Timeline

• 2020-12-09 - CVE CVE-2020-25627 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-25627

Vulnerability Analysis

This vulnerability is classified as CWE-79 (Improper Neutralization of Input During Web Page Generation), commonly known as Cross-Site Scripting. The flaw exists in how Moodle handles user-supplied input in the moodlenetprofile field, which is used to store Moodle.net profile information.

The vulnerability requires user interaction—a victim must view a page containing the malicious profile content for the attack to succeed. When exploited, the injected script runs within the context of the victim's authenticated session, potentially allowing attackers to steal session cookies, redirect users to malicious sites, or perform unauthorized actions within the Moodle platform.

The scope is changed, meaning the vulnerability in Moodle can impact resources beyond the vulnerable component itself, such as the user's browser or other web applications accessed in the same session.

Root Cause

The root cause of this vulnerability is insufficient input sanitization in the moodlenetprofile user profile field. When users enter data into this field, Moodle failed to properly encode or filter potentially dangerous HTML and JavaScript content before storing it in the database and rendering it on profile pages.

Stored XSS vulnerabilities are particularly dangerous in learning management systems like Moodle because:

• User profiles are frequently viewed by instructors, administrators, and other students
• Educational platforms often have privileged users with elevated access rights
• The persistent nature of stored XSS means the attack payload remains active until manually removed

Attack Vector

The attack vector is network-based, requiring no special privileges to exploit. An attacker would:

1. Create or modify a Moodle user account
2. Navigate to the profile settings containing the moodlenetprofile field
3. Insert malicious JavaScript code into the field instead of a legitimate Moodle.net profile URL
4. Save the profile changes

When another user views the attacker's profile page, the malicious script executes in their browser context. This could be used to:

• Hijack user sessions by stealing authentication cookies
• Perform actions as the victim user (such as changing grades if the victim is an instructor)
• Redirect users to phishing pages
• Deface content visible to the victim

The vulnerability does not require authentication to trigger (only to plant the payload), and the attack complexity is low, making this accessible to attackers with minimal technical expertise.

Detection Methods for CVE-2020-25627

Indicators of Compromise

• Unusual JavaScript content stored in user profile moodlenetprofile fields in the Moodle database
• Profile fields containing HTML tags such as <script>, <img onerror=, <svg onload=, or other event handlers
• Unexpected outbound connections originating from client browsers when viewing user profiles
• Reports from users about browser redirects or pop-ups when viewing certain profiles

Detection Strategies

• Implement database queries to scan the moodlenetprofile field for suspicious patterns including script tags and JavaScript event handlers
• Deploy Web Application Firewall (WAF) rules to detect and block XSS payloads in form submissions
• Enable Content Security Policy (CSP) headers to restrict script execution and receive violation reports
• Monitor server logs for unusual patterns in profile update requests

Monitoring Recommendations

• Configure browser Content Security Policy violation reporting to identify potential XSS attempts
• Implement real-time alerting for database modifications to user profile fields containing script-like content
• Review access logs for profiles that receive unusually high view counts, which may indicate attackers testing their payload
• Deploy endpoint detection to identify session token exfiltration attempts

How to Mitigate CVE-2020-25627

Immediate Actions Required

• Upgrade Moodle to version 3.9.2 or later immediately
• Audit existing user profiles for malicious content in the moodlenetprofile field
• Review administrator and instructor accounts for signs of compromise
• Implement Content Security Policy headers to mitigate impact of any existing stored XSS

Patch Information

Moodle has released version 3.9.2 which addresses this vulnerability by implementing proper input sanitization for the moodlenetprofile user profile field. Organizations should upgrade to this version or later as soon as possible.

For detailed patch information and the official security announcement, see the Moodle Discussion Forum.

Workarounds

• If immediate patching is not possible, consider disabling or hiding the moodlenetprofile field through Moodle's user profile field configuration
• Implement strict Content Security Policy headers with script-src 'self' to prevent inline script execution
• Deploy a Web Application Firewall (WAF) with XSS filtering rules in front of the Moodle installation
• Sanitize existing profile data by running database queries to identify and clean potentially malicious entries

# Example: Database query to identify potentially malicious moodlenetprofile entries
# Run this in your Moodle database to find suspicious content
SELECT id, userid, data FROM mdl_user_info_data 
WHERE fieldid = (SELECT id FROM mdl_user_info_field WHERE shortname = 'moodlenetprofile')
AND (data LIKE '%<script%' OR data LIKE '%javascript:%' OR data LIKE '%onerror%' OR data LIKE '%onload%');