CVE-2025-13766: MasterStudy LMS Auth Bypass Vulnerability

CVE-2025-13766 Overview

The MasterStudy LMS WordPress Plugin – for Online Courses and Education is vulnerable to unauthorized modification and deletion of data due to missing capability checks on multiple REST API endpoints. This Authorization Bypass vulnerability affects all versions up to and including 3.7.6, enabling authenticated attackers with Subscriber-level access and above to perform unauthorized actions on WordPress sites running the vulnerable plugin.

Critical Impact

Authenticated attackers with minimal privileges (Subscriber-level) can upload or delete arbitrary media files, delete or modify posts, and create/manage course templates without proper authorization.

Affected Products

• MasterStudy LMS WordPress Plugin versions up to and including 3.7.6
• WordPress sites utilizing MasterStudy LMS for online courses and education

Discovery Timeline

• 2026-01-06 - CVE CVE-2025-13766 published to NVD
• 2026-01-08 - Last updated in NVD database

Technical Details for CVE-2025-13766

Vulnerability Analysis

This vulnerability stems from CWE-862 (Missing Authorization), a critical security flaw where the application fails to perform authorization checks before allowing users to access protected functionality. The MasterStudy LMS plugin exposes multiple REST API endpoints that lack proper capability verification, allowing users with minimal authentication (Subscriber-level accounts) to perform administrative actions.

The vulnerability is network-accessible and requires low attack complexity, making it relatively easy for malicious actors to exploit. While it requires authentication, even the lowest privilege level (Subscriber) is sufficient to exploit the vulnerability. The impact includes both confidentiality and integrity concerns, as attackers can access, modify, and delete content they should not have permissions to touch.

Root Cause

The root cause lies in missing capability checks on multiple REST API endpoints within the MasterStudy LMS plugin. WordPress implements a robust roles and capabilities system designed to restrict user actions based on their assigned permissions. However, the vulnerable REST API endpoints in MasterStudy LMS fail to verify whether the requesting user has the appropriate capabilities before processing requests.

When a REST API request is made, the plugin should validate that the authenticated user possesses the necessary capabilities (such as upload_files, edit_posts, delete_posts, or custom capabilities for course management). The absence of these checks allows any authenticated user, regardless of their role, to perform actions typically reserved for administrators or editors.

Attack Vector

The attack vector is network-based, requiring an authenticated session with at least Subscriber-level access. An attacker would:

1. Register or obtain access to a Subscriber-level account on the target WordPress site
2. Identify the vulnerable REST API endpoints exposed by the MasterStudy LMS plugin
3. Craft malicious REST API requests to upload, modify, or delete content
4. Execute unauthorized actions such as uploading arbitrary media files, modifying or deleting posts, and managing course templates

The vulnerability allows attackers to bypass the intended access control mechanisms, effectively escalating their privileges without proper authorization verification. For detailed technical information, refer to the Wordfence Vulnerability Report.

Detection Methods for CVE-2025-13766

Indicators of Compromise

• Unusual REST API activity from low-privilege user accounts targeting MasterStudy LMS endpoints
• Unexpected media file uploads or deletions attributed to Subscriber-level users
• Unauthorized modifications to posts or course templates by users without appropriate permissions
• Anomalous patterns in WordPress audit logs showing administrative actions from non-admin accounts

Detection Strategies

• Monitor WordPress REST API logs for requests to MasterStudy LMS endpoints from users with Subscriber or Contributor roles
• Implement Web Application Firewall (WAF) rules to detect and alert on suspicious REST API activity patterns
• Review user activity logs for post modifications, media uploads, or course template changes by unauthorized users
• Deploy endpoint monitoring to track API calls and flag capability mismatches

Monitoring Recommendations

• Enable detailed logging for all REST API endpoints, particularly those exposed by the MasterStudy LMS plugin
• Configure real-time alerting for administrative actions performed by low-privilege users
• Regularly audit user permissions and role assignments to identify potential abuse vectors
• Implement SentinelOne Singularity to detect anomalous behavior patterns indicative of privilege abuse

How to Mitigate CVE-2025-13766

Immediate Actions Required

• Update the MasterStudy LMS WordPress Plugin to a patched version beyond 3.7.6 immediately
• Audit all user accounts and remove unnecessary Subscriber or higher-level accounts until patched
• Review recent activity logs for signs of exploitation or unauthorized content modifications
• Temporarily disable the MasterStudy LMS plugin if an immediate update is not possible

Patch Information

A security patch addressing this vulnerability is available. The WordPress Changeset Update contains the fix implementing proper capability checks on the affected REST API endpoints. Site administrators should update to the latest version of the MasterStudy LMS plugin to remediate this vulnerability.

For comprehensive vulnerability details and ongoing tracking, consult the Wordfence Vulnerability Report.

Workarounds

• Restrict user registration to prevent creation of new Subscriber accounts until patched
• Implement additional authorization controls via security plugins that enforce capability checks at the WAF level
• Use .htaccess or server configuration to restrict access to vulnerable REST API endpoints
• Monitor and limit REST API access using WordPress security plugins with API firewall capabilities

# Example: Restrict REST API access to administrators only via .htaccess
# Add to WordPress root .htaccess file (temporary workaround)
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteCond %{REQUEST_URI} ^/wp-json/masterstudy-lms/ [NC]
RewriteCond %{HTTP_COOKIE} !wordpress_logged_in [NC]
RewriteRule .* - [F,L]
</IfModule>