CVE-2025-64209

Executive Summary

CVE-2025-64209 is a Missing Authorization vulnerability (CWE-862) in the Masterstudy WordPress plugin developed by StylemixThemes. This flaw allows unauthenticated attackers to access functionality that should be properly constrained by Access Control Lists (ACLs). The vulnerability affects all versions of Masterstudy prior to 4.8.122. With a CVSS score of 7.5 (High), the primary impact is on confidentiality, as an attacker can potentially read sensitive data or perform unauthorized actions without needing any privileges. No public proof-of-concept (PoC) or exploit code is currently available, but the risk remains significant due to the plugin's widespread use in educational and LMS WordPress sites.

Supply Chain & Package Security

This vulnerability resides in a WordPress plugin distributed via the official WordPress plugin repository. The supply chain risk is elevated because:

• No patch is yet available from the vendor.
• The plugin is widely used in e-learning environments, making it a high-value target for data exfiltration.
• Attackers may target outdated installations via automated scanners.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
• Base Score: 7.5 (High)
• Attack Vector: Network (AV:N) – exploitable remotely.
• Attack Complexity: Low (AC:L) – no special conditions required.
• Privileges Required: None (PR:N) – no authentication needed.
• User Interaction: None (UI:N) – no victim action required.
• Scope: Unchanged (S:U) – vulnerability does not affect other components.
• Confidentiality Impact: High (C:H) – sensitive data can be accessed.
• Integrity Impact: None (I:N) – no data modification.
• Availability Impact: None (A:N) – no denial of service.

Threat Level: High. The combination of network exploitability, no required privileges, and high confidentiality impact makes this a critical risk for unpatched WordPress sites.

Deep Dive & Mechanics

The vulnerability stems from a missing authorization check in one or more AJAX actions or REST API endpoints within the Masterstudy plugin. The plugin likely exposes functions that handle course data, user profiles, or administrative operations without verifying that the requesting user has the appropriate capabilities (e.g., manage_options, edit_posts).

Root Cause Analysis:

• The plugin registers AJAX hooks (e.g., wp_ajax_* and wp_ajax_nopriv_*) or REST routes.
• For certain actions, the wp_ajax_nopriv_* hook (which allows unauthenticated access) is used, but the corresponding function does not perform a capability check.
• Alternatively, a REST endpoint may lack a permission_callback or use a non-restrictive one.

Attack Vector: An attacker sends a crafted HTTP request to the vulnerable endpoint. For example:

POST /wp-admin/admin-ajax.php HTTP/1.1
Host: target-site.com
Content-Type: application/x-www-form-urlencoded

action=masterstudy_get_sensitive_data&user_id=1

If the masterstudy_get_sensitive_data action lacks authorization, the attacker can retrieve private user data, course materials, or configuration details.

Impact:

• Unauthorized access to student records, instructor data, or payment information.
• Potential privilege escalation if the endpoint allows modifying user roles or settings.
• Data leakage that could lead to further targeted attacks.

Vulnerable vs. Patched Code

Since no official patch is available, the following is a hypothetical comparison based on common fixes for CWE-862.

Vulnerable Code (example):

add_action('wp_ajax_nopriv_masterstudy_get_data', 'masterstudy_get_data_handler');
function masterstudy_get_data_handler() {
    $user_id = $_GET['user_id'];
    $user_data = get_userdata($user_id);
    wp_send_json($user_data);
}

Patched Code (expected):

add_action('wp_ajax_nopriv_masterstudy_get_data', 'masterstudy_get_data_handler');
function masterstudy_get_data_handler() {
    // Add capability check
    if (!current_user_can('read')) {
        wp_die('Unauthorized', 403);
    }
    $user_id = intval($_GET['user_id']);
    // Ensure user can only access their own data
    if (get_current_user_id() !== $user_id && !current_user_can('edit_users')) {
        wp_die('Unauthorized', 403);
    }
    $user_data = get_userdata($user_id);
    wp_send_json($user_data);
}

Key Differences:

• The patched version adds current_user_can() checks.
• It validates that the requesting user owns the data or has elevated privileges.
• Input sanitization (intval()) is applied.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• A WordPress site running Masterstudy < 4.8.122.
• No authentication required.

Exploitation Steps:

1. Identify Vulnerable Endpoint: Use a tool like Burp Suite or curl to probe for AJAX actions. Common patterns include masterstudy_* or stm_*.
2. Craft Request: Send a POST request to /wp-admin/admin-ajax.php with the action parameter.
3. Extract Data: If successful, the response will contain sensitive information.

Example Exploit (curl):

curl -X POST https://target-site.com/wp-admin/admin-ajax.php \
  -d "action=masterstudy_get_user_data&user_id=1" \
  -H "Content-Type: application/x-www-form-urlencoded"

Expected Output:

{
  "ID": "1",
  "user_login": "admin",
  "user_email": "admin@example.com",
  "display_name": "Admin User",
  "roles": ["administrator"]
}

Blue Team (Detection & Hardening)

Detection:

• Monitor for unusual POST requests to /wp-admin/admin-ajax.php with unknown or suspicious action parameters.
• Look for requests from IPs that are not associated with legitimate users.
• Check for repeated attempts to access user data without authentication.

Hardening:

• Immediate: Disable the Masterstudy plugin until a patch is available.
• Workaround: Use a Web Application Firewall (WAF) to block requests to unknown AJAX actions.
• Long-term: Apply the principle of least privilege to all plugin endpoints.

Indicators of Compromise (IOCs)

Network IOCs:

• POST requests to /wp-admin/admin-ajax.php with action=masterstudy_* parameters from unauthenticated sources.
• HTTP 200 responses containing JSON with user data (e.g., user_email, user_login).

File IOCs:

• Modified plugin files in /wp-content/plugins/masterstudy/ (check file integrity).
• Suspicious log entries in /wp-content/debug.log showing unauthorized access attempts.

Behavioral IOCs:

• Unusual spikes in AJAX requests to the vulnerable endpoint.
• Access to user data endpoints from IPs not associated with known users.

Detection Engineering

YARA Rule

rule CVE_2025_64209_Masterstudy_Auth_Bypass {
    meta:
        description = "Detects exploitation attempts for CVE-2025-64209 in Masterstudy plugin"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-64209"
    strings:
        $ajax_action = /action=masterstudy_[a-z_]+/
        $user_id_param = /user_id=\d+/
        $sensitive_response = /"user_email":/
    condition:
        $ajax_action and $user_id_param and #sensitive_response > 0
}

Sigma Rule

title: CVE-2025-64209 Masterstudy Missing Authorization Exploitation
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects unauthenticated access to Masterstudy AJAX endpoints
author: Valters IT
date: 2025/04/10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        c-uri: '/wp-admin/admin-ajax.php'
        cs-uri-query|contains: 'action=masterstudy_'
        sc-status: 200
    condition: selection
falsepositives:
    - Legitimate plugin functionality (rare)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2025-64209 Masterstudy Missing Authorization Exploitation";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"/wp-admin/admin-ajax.php"; http_uri;
    content:"action=masterstudy_"; http_client_body;
    classtype:attempted-recon;
    sid:10000001;
    rev:1;
)

Remediation & Mitigation

Immediate Actions:

1. Disable the Masterstudy plugin if it is not critical to operations.
2. Apply virtual patching via WAF rules to block requests to unknown AJAX actions.
3. Monitor logs for exploitation attempts.

Long-term Fix:

• Update to version 4.8.122 or later once the vendor releases a patch.
• Implement a WordPress security plugin (e.g., Wordfence) to add an extra layer of authorization checks.
• Conduct a code review of all custom AJAX endpoints to ensure proper capability checks.

Workaround Code (if patching is delayed): Add the following to your theme's functions.php to block unauthenticated access to Masterstudy AJAX actions:

add_action('init', function() {
    if (defined('DOING_AJAX') && DOING_AJAX && !is_user_logged_in()) {
        $action = $_REQUEST['action'] ?? '';
        if (strpos($action, 'masterstudy_') === 0) {
            wp_die('Unauthorized', 403);
        }
    }
});

Valters IT
Securing Digital Frontiers