CVE-2026-34370: Chamilo LMS IDOR Vulnerability

CVE-2026-34370 Overview

CVE-2026-34370 is an Insecure Direct Object Reference (IDOR) vulnerability affecting Chamilo LMS, an open-source learning management system. The vulnerability exists in the notebook module and allows any authenticated student to read the private course notes of any other user on the platform by manipulating the notebook_id parameter in the editnote action. The application fetches the note content using only the supplied integer ID without verifying that the requesting user owns the note, exposing the full title and HTML body in the edit form to unauthorized users.

Critical Impact

Authenticated attackers can access private course notes belonging to any user on the platform, potentially exposing sensitive educational content, personal notes, and confidential course materials.

Affected Products

• Chamilo LMS versions prior to 2.0.0-RC.3

Discovery Timeline

• 2026-04-14 - CVE CVE-2026-34370 published to NVD
• 2026-04-14 - Last updated in NVD database

Technical Details for CVE-2026-34370

Vulnerability Analysis

This Insecure Direct Object Reference vulnerability stems from inconsistent authorization enforcement across different code paths in the Chamilo LMS notebook module. The vulnerability allows authenticated users with student privileges to access private notes belonging to other users through direct parameter manipulation.

The exploitation mechanism is straightforward: an attacker simply needs to modify the notebook_id parameter value in requests to the editnote action. Since the application directly queries the database using the provided ID without ownership validation, any valid note ID will return the corresponding note content regardless of who owns it.

While the development team implemented proper ownership validation in the write operations (updateNote() and delete_note() functions), this critical check was entirely omitted from the read path (get_note_information() function). This inconsistency represents a common vulnerability pattern where different code paths handling the same resource have varying levels of access control.

Root Cause

The root cause is a missing authorization check in the get_note_information() function. Unlike the updateNote() and delete_note() functions which properly verify that the requesting user owns the note before performing operations, the read path fetches and returns note content based solely on the notebook_id parameter without any ownership verification. This is classified as CWE-285 (Improper Authorization).

Attack Vector

The attack is network-based and requires only low-privilege authenticated access. An attacker who has registered as a student on the Chamilo LMS platform can enumerate notebook_id values and retrieve private notes from any user, including instructors, administrators, and other students.

The attack flow involves:

1. Authenticating to the Chamilo LMS platform with valid student credentials
2. Navigating to the notebook edit functionality
3. Manipulating the notebook_id parameter to reference notes owned by other users
4. Receiving the full title and HTML body of the targeted note in the edit form response

Since the vulnerability requires only basic authentication without additional privileges, the barrier to exploitation is minimal. See the GitHub Security Advisory GHSA-fm35-2hvw-564q for complete technical details.

Detection Methods for CVE-2026-34370

Indicators of Compromise

• Unusual access patterns to the notebook editnote action with rapidly changing notebook_id values
• Single user sessions accessing note IDs that do not belong to their account
• Sequential or enumerated requests to notebook endpoints suggesting automated scanning
• Error logs showing failed authorization checks on related write operations while read operations succeed

Detection Strategies

• Implement application-level logging that captures user ID alongside requested notebook_id values for audit purposes
• Monitor web application logs for enumeration patterns in notebook-related endpoints
• Review access logs for users accessing an abnormally high number of different note IDs
• Deploy web application firewall (WAF) rules to detect parameter tampering on sensitive endpoints

Monitoring Recommendations

• Enable detailed audit logging for all notebook module operations including read access
• Configure alerting for access attempts to notes owned by other users
• Establish baseline metrics for normal notebook access patterns per user
• Review authentication and session logs for accounts exhibiting suspicious notebook access behavior

How to Mitigate CVE-2026-34370

Immediate Actions Required

• Upgrade Chamilo LMS to version 2.0.0-RC.3 or later immediately
• Review application logs for potential past exploitation of this vulnerability
• Audit notebook contents for any sensitive data that may have been exposed
• Consider notifying users if evidence of unauthorized access is discovered

Patch Information

The vulnerability has been addressed in Chamilo LMS version 2.0.0-RC.3. Organizations should upgrade to this version or later as soon as possible. The patch adds proper ownership validation to the get_note_information() function, ensuring that users can only access their own notes.

For detailed information about the fix, refer to:

• GitHub Release v2.0.0-RC.3
• GitHub Security Advisory GHSA-fm35-2hvw-564q

Workarounds

• Restrict access to the notebook module at the web server level until patching is complete
• Implement additional authentication layers or IP restrictions for notebook functionality
• Consider temporarily disabling the notebook feature if it is not critical to operations
• Deploy a web application firewall (WAF) rule to block requests to the editnote action while awaiting the patch