CVE-2026-33707: Chamilo LMS Auth Bypass Vulnerability

CVE-2026-33707 Overview

CVE-2026-33707 is a critical Weak Authentication vulnerability affecting Chamilo LMS, a popular open-source learning management system used by educational institutions and organizations worldwide. The vulnerability exists in the password reset mechanism, which generates predictable tokens using sha1($email) without any random component, token expiration, or rate limiting. This design flaw allows an attacker who knows a user's email address to compute the password reset token and change the victim's password without any authentication.

Critical Impact

An unauthenticated attacker can take over any user account in a Chamilo LMS installation by computing the predictable password reset token from a known email address, leading to complete account compromise including administrator accounts.

Affected Products

• Chamilo LMS versions prior to 1.11.38
• Chamilo LMS 2.0.0-alpha1 through 2.0.0-alpha5
• Chamilo LMS 2.0.0-beta1 through 2.0.0-beta3
• Chamilo LMS 2.0.0-rc1 and 2.0.0-rc2

Discovery Timeline

• April 10, 2026 - CVE-2026-33707 published to NVD
• April 16, 2026 - Last updated in NVD database

Technical Details for CVE-2026-33707

Vulnerability Analysis

This vulnerability is classified under CWE-640 (Weak Password Recovery Mechanism for Forgotten Password). The password reset functionality in Chamilo LMS prior to version 1.11.38 and 2.0.0-RC.3 implements a fundamentally flawed token generation mechanism. The system uses a deterministic approach where the reset token is simply the SHA-1 hash of the user's email address. This means anyone who knows a user's email can independently calculate the exact same token that the system generates.

The vulnerability is compounded by three additional security weaknesses: the tokens never expire, there is no rate limiting on password reset attempts, and the token remains valid indefinitely until used. This creates a perfect storm for account takeover attacks where an attacker can target any account at their leisure without triggering security alerts.

Root Cause

The root cause lies in the get_secret_word() function within main/inc/lib/login.lib.php. This function generates password reset tokens using only the user's email address as input to SHA-1 hashing, with no cryptographically secure random component. The deterministic nature of hash functions means that the same input always produces the same output, making tokens entirely predictable to anyone who knows the email address.

Attack Vector

The attack can be executed remotely over the network without any authentication. An attacker simply needs to:

1. Identify a target user's email address (often publicly available or guessable)
2. Compute sha1(target_email) to generate the reset token
3. Craft a password reset URL with the computed token and target user ID
4. Navigate to the URL and set a new password for the victim's account

The following patch demonstrates the fix applied in the security update:

 
         if ($reset) {
             if ($by_username) {
-                $secret_word = self::get_secret_word($user['email']);
+                $token = self::generate_reset_token($user['uid']);
                 if ($reset) {
-                    $reset_link = $portal_url."main/auth/lostPassword.php?reset=".$secret_word."&id=".$user['uid'];
+                    $reset_link = $portal_url."main/auth/lostPassword.php?reset=".$token."&id=".$user['uid'];
                     $reset_link = Display::url($reset_link, $reset_link);
                 } else {
                     $reset_link = get_lang('Pass')." : $user[password]";

Source: GitHub Security Patch

Detection Methods for CVE-2026-33707

Indicators of Compromise

• Multiple password reset requests targeting different user accounts from the same IP address
• Password reset URL access patterns where the reset token matches sha1(email) patterns
• Unusual login activity following password reset events without legitimate user action
• Database queries showing password changes without corresponding email click-through tracking

Detection Strategies

• Implement web application firewall (WAF) rules to detect and alert on high-frequency password reset attempts
• Monitor authentication logs for password changes that occur immediately after reset requests from unfamiliar IP addresses
• Create SIEM rules to correlate password reset events with subsequent login attempts from different geographic locations
• Review access logs for direct navigation to password reset confirmation URLs without preceding reset request

Monitoring Recommendations

• Enable detailed logging for all password reset operations including IP addresses, timestamps, and user agents
• Set up alerting for administrator account password reset attempts
• Monitor for patterns of reset token usage that suggest predictable token exploitation
• Implement anomaly detection for account access patterns following password changes

How to Mitigate CVE-2026-33707

Immediate Actions Required

• Upgrade Chamilo LMS to version 1.11.38 or 2.0.0-RC.3 immediately
• Audit authentication logs for signs of exploitation and identify potentially compromised accounts
• Force password reset for all users using a secure out-of-band communication method
• Review and revoke any suspicious administrative account changes

Patch Information

Chamilo has released security patches that address this vulnerability by replacing the predictable get_secret_word() function with a new generate_reset_token() function that uses cryptographically secure random token generation. The patches are available in:

• Chamilo LMS 1.11.38 - View Commit for 1.11.x
• Chamilo LMS 2.0.0-RC.3 - View Commit for 2.x

For complete details, refer to the GitHub Security Advisory GHSA-f27g-66gq-g7v2.

Workarounds

• Disable the password reset functionality at the application level until patching is complete
• Implement network-level rate limiting on the password reset endpoint (/main/auth/lostPassword.php)
• Place the Chamilo LMS instance behind a reverse proxy with additional authentication controls
• Restrict access to the password reset functionality to specific trusted IP ranges if feasible

# Example Apache configuration to rate limit password reset endpoint
<Location "/main/auth/lostPassword.php">
    SetEnvIf Request_Method POST rate_limit
    # Implement rate limiting via mod_evasive or similar module
    # Consider blocking or challenging requests after threshold
</Location>