CVE-2026-30882: Chamilo LMS Reflected XSS Vulnerability

CVE-2026-30882 Overview

CVE-2026-30882 is a Reflected Cross-Site Scripting (XSS) vulnerability affecting Chamilo LMS, a popular open-source learning management system used by educational institutions worldwide. The vulnerability exists in the session category listing page where the keyword parameter from $_REQUEST is echoed directly into an HTML href attribute without proper encoding or sanitization. This allows attackers to inject arbitrary HTML and JavaScript code by breaking out of the attribute context.

Critical Impact

Attackers can execute arbitrary JavaScript in victim browsers, potentially stealing session cookies, performing actions on behalf of authenticated users, or redirecting users to malicious sites. Educational institutions running vulnerable Chamilo LMS versions are at risk of credential theft and data compromise.

Affected Products

• Chamilo LMS version 1.11.34 and prior
• All Chamilo LMS installations with session category functionality enabled
• Systems where the number of session categories exceeds 20 (triggering pagination controls)

Discovery Timeline

• 2026-03-16 - CVE CVE-2026-30882 published to NVD
• 2026-03-17 - Last updated in NVD database

Technical Details for CVE-2026-30882

Vulnerability Analysis

This Reflected XSS vulnerability occurs due to improper input validation in the session category listing functionality of Chamilo LMS. The application takes user-controlled input from the keyword parameter and directly embeds it into an HTML href attribute within the pagination controls without applying proper output encoding or sanitization.

The vulnerability is specifically triggered when pagination controls are rendered, which occurs when the number of session categories in the system exceeds 20 (the default page limit). This conditional triggering mechanism means the vulnerability may not be immediately apparent during basic security testing of installations with fewer session categories.

When exploited, an attacker can craft a malicious URL containing JavaScript payload that executes in the context of the victim's browser session. This can lead to session hijacking, credential theft, defacement of the LMS interface, or further attacks against authenticated users including administrators.

Root Cause

The root cause of this vulnerability is the direct inclusion of unsanitized user input from the $_REQUEST['keyword'] superglobal into HTML output. The application fails to apply proper context-aware output encoding when rendering the keyword value within an href attribute. Specifically, the value is not HTML entity encoded, allowing attackers to inject special characters like "> to break out of the attribute context and inject malicious HTML or script elements.

Attack Vector

The attack vector is network-based and requires user interaction. An attacker must craft a malicious URL containing the XSS payload in the keyword parameter and convince a victim to click the link. The attack flow typically involves:

1. Attacker identifies a vulnerable Chamilo LMS installation with more than 20 session categories
2. Attacker crafts a malicious URL with JavaScript payload in the keyword parameter using "> to escape the href attribute
3. Attacker distributes the malicious link via phishing emails, social media, or other channels
4. When a victim clicks the link while authenticated to the LMS, the JavaScript executes in their browser context

The vulnerability is exploited by injecting a payload such as "><script>malicious_code</script> into the keyword parameter, which breaks out of the href attribute and injects executable script content into the page.

Detection Methods for CVE-2026-30882

Indicators of Compromise

• Web server logs containing requests to session category pages with suspicious keyword parameter values containing HTML special characters (">, <script>, javascript:)
• Unusual URL patterns in referrer logs pointing to the session category listing endpoint with encoded payloads
• User reports of unexpected browser behavior or redirects when accessing Chamilo LMS

Detection Strategies

• Implement Web Application Firewall (WAF) rules to detect and block XSS patterns in the keyword parameter
• Deploy endpoint detection solutions to monitor for suspicious JavaScript execution patterns in browser contexts
• Configure log monitoring to alert on requests containing common XSS payload signatures targeting Chamilo endpoints
• Use SentinelOne Singularity to detect post-exploitation activities such as credential harvesting or unauthorized session access

Monitoring Recommendations

• Enable detailed access logging for the Chamilo LMS application, particularly for session management endpoints
• Monitor for abnormal patterns in authentication events that may indicate session hijacking following XSS exploitation
• Implement Content Security Policy (CSP) headers and monitor for CSP violation reports
• Review user activity logs for actions performed from unexpected IP addresses or locations

How to Mitigate CVE-2026-30882

Immediate Actions Required

• Upgrade Chamilo LMS to version 1.11.36 or later immediately
• Review access logs for evidence of exploitation attempts targeting the session category listing page
• Implement a Web Application Firewall with XSS filtering rules as a temporary protective measure
• Notify users to be cautious of clicking links to the LMS from untrusted sources

Patch Information

Chamilo has released version 1.11.36 which addresses this vulnerability. Organizations should upgrade to this version or later to remediate the issue. The patch properly encodes user input before rendering it in HTML contexts, preventing the attribute context breakout attack.

For detailed patch information, refer to the GitHub Release v1.11.36 and the GitHub Security Advisory GHSA-qg5f-gq95-9vhq.

Workarounds

• Implement strict input validation at the web server or reverse proxy level to reject requests containing HTML special characters in the keyword parameter
• Deploy Content Security Policy headers with strict script-src directives to mitigate the impact of XSS attacks
• Reduce the number of session categories below 20 to prevent pagination controls from rendering (temporary workaround only)
• Use a WAF rule to sanitize or block the keyword parameter until patching is complete

# Example Apache ModSecurity rule to block XSS attempts
SecRule ARGS:keyword "@rx (?i)(<script|javascript:|onerror|onload|\"[^\"]*>)" \
    "id:1001,phase:1,deny,status:403,msg:'Potential XSS in keyword parameter'"