CVE-2025-55289: Chamilo LMS Stored XSS Vulnerability

CVE-2025-55289 Overview

CVE-2025-55289 is a critical stored Cross-Site Scripting (XSS) vulnerability in Chamilo LMS, an open-source learning management system. Prior to version 1.11.34, the platform fails to properly sanitize user input in its social network and internal messaging features, allowing attackers to inject arbitrary JavaScript code. When the malicious payload is viewed by an authenticated user, including administrators, the injected script executes within the victim's browser session in the context of the LMS. This vulnerability enables attackers to perform full account takeover via session hijacking, execute unauthorized actions with the victim's privileges, exfiltrate sensitive data, and potentially propagate the attack to other users within the platform.

Critical Impact

This stored XSS vulnerability can lead to complete compromise of administrator accounts, unauthorized access to sensitive educational data, and self-propagating attacks across the entire LMS user base.

Affected Products

• Chamilo LMS versions prior to 1.11.34
• Chamilo LMS version 1.11.32 (specifically confirmed vulnerable)
• All Chamilo LMS installations using social network and internal messaging features

Discovery Timeline

• 2026-03-06 - CVE-2025-55289 published to NVD
• 2026-03-09 - Last updated in NVD database

Technical Details for CVE-2025-55289

Vulnerability Analysis

This stored XSS vulnerability (CWE-79) exists within the social network and internal messaging components of Chamilo LMS. The vulnerability arises from insufficient input validation and output encoding when processing user-generated content in these features. When a user submits content containing malicious JavaScript through the social network posts or internal messages, the application stores this content in the database without proper sanitization. Subsequently, when other users view this content, the malicious script executes in their browser context.

The cross-site nature of this attack is particularly severe because the scope is changed (indicated by the Changed scope in the vulnerability characteristics), meaning the vulnerable component and the impacted component are different. An attacker with low-privileged access to the platform can craft malicious payloads that, once viewed by administrators, execute with full administrative privileges in the browser context.

Root Cause

The root cause of CVE-2025-55289 is improper input validation and inadequate output encoding in Chamilo LMS's social network and messaging modules. The application accepts user input containing HTML and JavaScript without sanitizing potentially dangerous characters or tags. When this content is later rendered in users' browsers, the lack of proper output encoding allows the stored malicious scripts to execute. This represents a classic stored XSS pattern where user-controlled data is persisted to the database and later included in web pages without appropriate security controls.

Attack Vector

The attack is network-based and requires the attacker to have low-level authenticated access to the Chamilo LMS platform. The exploitation flow involves:

1. An attacker authenticates to the Chamilo LMS with a standard user account
2. The attacker crafts a malicious JavaScript payload designed to steal session tokens, perform actions, or propagate to other users
3. The payload is submitted through the social network feature (posts, comments) or internal messaging system
4. The malicious content is stored in the application database
5. When a victim user (including administrators) views the content, the JavaScript executes in their browser
6. The attacker gains access to the victim's session, can perform actions as the victim, or exfiltrate sensitive data

The vulnerability mechanism involves injecting JavaScript payloads into user-generated content fields. Without proper sanitization, these payloads persist in the database and execute when rendered to other users. See the GitHub Security Advisory GHSA-cchj-3qmf-82j5 for technical details on exploitation patterns.

Detection Methods for CVE-2025-55289

Indicators of Compromise

• Unusual JavaScript code patterns in database records for social network posts and internal messages
• Suspicious outbound network requests from client browsers to external domains when viewing LMS content
• Session tokens or cookies being transmitted to unexpected destinations in browser network logs
• User reports of unexpected behavior, pop-ups, or redirects when viewing social content or messages

Detection Strategies

• Implement Web Application Firewall (WAF) rules to detect and block common XSS payloads in POST requests to social network and messaging endpoints
• Monitor database tables for suspicious entries containing <script> tags, event handlers like onerror, onload, or JavaScript URI schemes
• Deploy Content Security Policy (CSP) headers to detect and report inline script execution attempts
• Review application logs for unusual patterns in content submission to social and messaging features

Monitoring Recommendations

• Enable CSP reporting to capture and alert on blocked inline script execution attempts
• Monitor for anomalous session activity that could indicate session hijacking following XSS exploitation
• Implement real-time alerting for multiple failed or suspicious login attempts following user browsing activity
• Track user-generated content for patterns matching known XSS payload signatures

How to Mitigate CVE-2025-55289

Immediate Actions Required

• Upgrade Chamilo LMS to version 1.11.34 or later immediately
• Review existing social network posts and internal messages for potentially malicious content
• Consider temporarily disabling social network and messaging features if immediate upgrade is not possible
• Invalidate all active sessions and require users to re-authenticate after patching

Patch Information

Chamilo has addressed this vulnerability in version 1.11.34. Organizations should upgrade to this version or later to remediate the vulnerability. The official release is available at the GitHub Release v1.11.34. Additional details about the security fix can be found in the GitHub Security Advisory GHSA-cchj-3qmf-82j5.

Workarounds

• Implement a Web Application Firewall (WAF) with rules to filter XSS payloads targeting social network and messaging endpoints
• Deploy strict Content Security Policy headers to prevent inline script execution: script-src 'self'
• Restrict access to social network and messaging features to trusted users only until patching is complete
• Implement additional server-side input validation for user-generated content as a defense-in-depth measure

# Example Apache configuration to add CSP headers as temporary mitigation
<IfModule mod_headers.c>
    Header set Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline'; img-src 'self' data:; frame-ancestors 'self';"
    Header set X-XSS-Protection "1; mode=block"
    Header set X-Content-Type-Options "nosniff"
</IfModule>