Plugin Name	MasterStudy LMS
Type of Vulnerability	Access control vulnerability
CVE Number	CVE-2025-13766
Urgency	Low
CVE Publish Date	2026-01-05
Source URL	CVE-2025-13766

MasterStudy LMS ≤ 3.7.6 – Broken Access Control Vulnerability (CVE-2025-13766): Insights and How Managed-WP Shields Your WordPress

By Managed-WP Security Team | 2026-01-05 | Categories: WordPress Security, Vulnerability Response, Managed WAF

Executive Summary

On January 5, 2026, a critical access control vulnerability was publicly disclosed affecting MasterStudy LMS for WordPress versions 3.7.6 and earlier. Identified as CVE-2025-13766, this flaw permits authenticated users with Subscriber privileges to create, modify, and delete posts and media—actions normally restricted to higher privilege roles—due to missing authorization validations.

Scored at 5.4 CVSS for broken access control, this issue can expose your site to content manipulation, unwanted media uploads, and potential downstream attacks. MasterStudy LMS 3.7.7 addresses this vulnerability. We strongly advise immediate updates. If updating right now isn’t feasible, implement the mitigation steps below. Managed-WP delivers comprehensive guidance and virtual patching strategies to reduce your risk exposure efficiently.

---

Technical Background: What the Vulnerability Entails

Security researchers uncovered that MasterStudy LMS plugin endpoints and AJAX handlers lack proper permission checks and nonce verification, permitting subscriber accounts to execute restricted operations such as post and media creation or deletion.

Key Details:

• Plugin: MasterStudy LMS
• Affected Versions: ≤ 3.7.6
• Patched Version: 3.7.7
• CVE ID: CVE-2025-13766
• Vulnerability Type: Broken Access Control (OWASP A1)
• Exploit Prerequisite: Authenticated Subscriber Role
• Disclosure Date: 2026-01-05

While requiring an authenticated user lowers the severity relative to fully unauthenticated bugs, many WordPress LMS sites allow user registration with the subscriber role, turning this into a practical risk for registrations or community-driven platforms.

---

Implications for WordPress Site Operators

WordPress’s multi-user environment depends on accurate enforcement of user capabilities. Plugins exposing REST API or AJAX endpoints without strict authorization allow attackers to leverage low-privileged user accounts to escalate actions.

Potential risks include:

• Creation of malicious posts or pages to serve spam, phishing, or SEO manipulation.
• Uploading harmful executables disguised as media potentially leading to malware or backdoors.
• Modification or deletion of course content, impacting learning integrity and site operations.
• Privilege escalation via chained vulnerabilities following unauthorized content injections.

Due to access to post and media management, attackers could covertly undermine your site’s reputation and technical security.

---

Attack Methodology

An adversary can exploit the flaw by:

1. Registering a subscriber account or leveraging an existing low-privilege account.
2. Identifying vulnerable REST or AJAX endpoints exposed by the plugin.
3. Sending crafted POST, PUT, or DELETE requests to create, modify, or delete content/media, bypassing authorization checks.
4. Utilizing compromised posts or media for malicious campaigns or pivoting to deeper system compromises.

This attack requires no complex privilege escalation, relying only on authenticated access and knowledge of vulnerable endpoints, making it highly effective, especially on sites with open registration.

---

How to Detect Signs of Exploitation

Check your site for these indicators if using affected MasterStudy LMS versions:

• Posts, pages, or attachments created or edited by Subscriber-role users. Run this SQL query for forensic insight:

SELECT ID, post_title, post_type, post_date, post_author
FROM wp_posts
WHERE post_author IN (
  SELECT ID FROM wp_users WHERE ID IN (
    SELECT user_id FROM wp_usermeta WHERE meta_key = 'wp_capabilities' AND meta_value LIKE '%subscriber%'
  )
)
ORDER BY post_date DESC;

• Unexpected files, especially PHP or suspicious scripts, within your uploads directory.
• Unexplained recent modifications to media library items.
• Suspicious new subscriber accounts created around the same time.
• Unusual POST/PUT/DELETE activity targeting REST endpoints or admin-ajax.php in server logs.

Utilize activity logging plugins and malware scanners to perform thorough audits.

---

Immediate Mitigations If You Cannot Update Immediately

1. Update the plugin to version 3.7.7 ASAP. It is the definitive fix.
2. Temporarily restrict Subscriber capabilities: Add this code to a site-specific plugin or theme functions.php:

// Block subscribers from content manipulation and file uploads temporarily
add_action('init', function() {
    if ( get_role('subscriber') ) {
        $role = get_role('subscriber');
        $caps_to_remove = [
            'edit_posts',
            'delete_posts',
            'publish_posts',
            'upload_files',
            'edit_published_posts',
            'delete_published_posts'
        ];
        foreach ($caps_to_remove as $cap) {
            if ($role->has_cap($cap)) {
                $role->remove_cap($cap);
            }
        }
    }
});

Note: This might break legitimate LMS functions for Subscribers, so test carefully.

3. Block plugin REST and AJAX endpoints via WAF or server rules: For example, Apache .htaccess to block REST calls containing “masterstudy”:

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteCond %{REQUEST_URI} ^/wp-json/ [NC]
RewriteCond %{REQUEST_URI} masterstudy [NC]
RewriteRule .* - [F,L]
</IfModule>

4. Apply a temporary REST filter in WordPress to deny access for non-admins to plugin routes:

add_filter('rest_pre_dispatch', function($result, $server, $request) {
    $route = $request->get_route();
    if (strpos($route, 'masterstudy') !== false) {
        if (!current_user_can('manage_options')) {
            return new WP_Error('rest_forbidden', 'Restricted', array('status' => 403));
        }
    }
    return $result;
}, 10, 3);

5. Disable any front-end file uploads available to Subscribers until patched.
6. Force password resets for privileged accounts and review recent user registrations for anomalies.
7. Back up your full site and database before making further changes or remediations.

---

How Managed-WP Fortifies Your Site

Managed-WP delivers multi-layer defense mechanisms tailored for rapid response to plugin vulnerabilities:

1. Virtual Patching: Dynamic firewall rules block malicious HTTP requests targeting plugin endpoints, buying you critical time to update securely.
2. Behavior-Based Controls: Monitoring and blocking suspicious low-privilege account activities on protected REST routes.
3. Role-Aware Restrictions: Seamlessly restrict specific WordPress roles from accessing sensitive plugin namespaces and AJAX actions.
4. Upload Inspection: Automated scans detect and quarantine potentially malicious media uploads in real-time.
5. Comprehensive Rate Limiting: Preempt large-scale abuse through throttling and temporary blocks.
6. Alerts and Reporting: Real-time notifications and forensic logging for suspicious activities.
7. Managed Auto-Updates & Support: Proactive patch notifications and, where available, automated plugin upgrades to keep you secure.

If you are already on Managed-WP, enable virtual patching now and perform a full security audit. If not, join us to get immediate protection.

---

Sample Firewall Rule Concepts to Implement

These conceptual patterns guide custom WAF configurations or Managed-WP firewall policies and should be tested in staging environments before production:

• Block POST/PUT/DELETE to plugin REST namespaces:
  • Match requests with methods POST, PUT or DELETE
  • Request path matches regex ^/wp-json/.*/(masterstudy|stm|mslms).*
  • Action: block or challenge with 403 or CAPTCHA
• Block suspicious admin-ajax.php calls:
  • Request path is /wp-admin/admin-ajax.php
  • Request param action matches plugin’s sensitive actions
  • Authenticated requests not whitelisted
  • Action: block or throttle
• Rate-limit REST endpoint abuse:
  • Detect X or more POST requests to plugin REST paths within Y seconds from same IP
  • Action: gradual throttling followed by temporary block
• Quarantine suspicious uploads:
  • Block uploads with mismatched MIME types & suspicious extensions e.g., php, phtml, exe
  • Action: block upload, quarantine file, notify admin

Important: Avoid blanket REST blocking. Test all firewall rules thoroughly to prevent false positives and service disruption.

---

Best Practices for Long-Term WordPress Security Hardening

1. Enforce the Principle of Least Privilege: Subscribers should only have minimal capabilities (read-only wherever possible).
2. Disable Public Registration: Turn off user sign-ups if not required for your platform.
3. Audit Plugin Code: Review AJAX and REST APIs for proper authorization checks before deploying plugins.
4. Use Capability-Based Filters: Add REST API filters proactively restricting untrusted user roles.
5. Implement File Integrity Monitoring: Detect unexpected file additions or changes in wp-content.
6. Harden Upload Folders: Prevent PHP execution under wp-content/uploads with web server rules, for example:

<Directory "/var/www/html/wp-content/uploads">
    <FilesMatch "\.php$">
        Require all denied
    </FilesMatch>
</Directory>

7. Deploy a WAF With Virtual Patching Features: This reduces exposure during vulnerability windows.
8. Enable Logging and Alerts: Monitor for anomalous low-privilege activities and irregular upload spikes.
9. Maintain Regular Backups and a Staging Environment: Test updates and patches safely before production rollout.

---

Recovery Guidance if Your Site Has Been Compromised

1. Take your site offline or display a maintenance page immediately.
2. Preserve system logs and take a full backup of files and database for forensic analysis.
3. Assess the scope: identify affected users, posts, and files.
4. Restore from a known clean backup if available, ideally predating the compromise.
5. Remove malicious content manually if restoring is not feasible.
6. Reset all administrator passwords; rotate API keys and secrets.
7. Scan thoroughly for web shells and backdoors, looking for obfuscated code or unexpected files.
8. Remove unused or vulnerable plugins/themes and update all active components.
9. Harden wp-config.php to disable file editing:

define('DISALLOW_FILE_EDIT', true);
define('DISALLOW_FILE_MODS', true);

10. Reinstate protections and monitor your site closely for recurring issues.

If you lack the expertise for a forensic investigation and cleanup, Managed-WP offers expert managed remediation services on premium plans.

---

Temporary REST API Filter Example to Block MasterStudy Endpoints for Non-Admins

Insert this snippet into a site-specific plugin (remove after patching):

<?php
/*
Plugin Name: Temporary MasterStudy REST Blocker
Description: Emergency filter blocking MasterStudy REST endpoints for non-admins.
Author: Managed-WP Security Team
Version: 1.0
*/

add_filter('rest_pre_dispatch', function($result, $server, $request) {
    $route = $request->get_route();
    if (strpos($route, '/masterstudy') !== false || strpos($route, '/stm') !== false) {
        if (!current_user_can('manage_options')) {
            return new WP_Error('rest_forbidden', 'This endpoint is temporarily restricted.', array('status' => 403));
        }
    }
    return $result;
}, 10, 3);

After upgrading to 3.7.7 or later, remove this plugin and test all functionality.

---

Key Takeaways for WordPress Site Operators

• Identify plugins permitting frontend uploads or content creation as higher risk and vet thoroughly.
• Ensure you have a clear, rapid path to patching vulnerabilities promptly.
• Combine automated defenses like WAF and malware scanning with routine audits and user role reviews.
• Adopt a “blast radius” mindset—minimize the impact of compromised accounts by restricting privileges.

---

Media and Upload Folder Protection Best Practices

• Restrict executable files in uploads; enforce strict MIME and file extension validation.
• Use server rules to block direct execution and enforce downloads of suspicious file types.
• Integrate malware scanning on uploads to catch threats early.

---

Get Started with Managed-WP Free Plan for Essential Protection

Immediate WordPress Security—Simplified

Managed-WP offers a free security plan providing essential firewall protection including a Web Application Firewall (WAF), malware scanning, and mitigation against top OWASP risks. This first layer helps guard your site while applying patches and hardening configurations.

Sign up for the free plan and enable virtual patching in minutes: https://my.wp-firewall.com/buy/wp-firewall-free-plan/

Upgrade anytime for advanced features like auto-remediation, custom firewall policies, and expert support.

---

Recommended Immediate Actions for Site Owners

1. Confirm your MasterStudy LMS plugin version; if ≤ 3.7.6, schedule urgent maintenance.
2. Update to version 3.7.7 without delay.
3. If update is delayed, apply emergency mitigations: capability restrictions, REST filters, and firewall rules.
4. Conduct a full malware scan; review suspicious content authored by subscribers.
5. Rotate credentials for all admin users; audit API tokens and access keys.
6. Monitor logs vigilantly for repeated attack attempts or unusual activities.
7. Enable Managed-WP protection now, starting with the free plan, and activate virtual patching.

---

Why Quick Mitigation Is Crucial

Broken access control vulnerabilities let attackers wield low-level accounts as stepping stones to compromise your site through content injection, malware uploads, and privilege escalations. The resulting damage includes SEO poisoning, customer trust loss, and data breaches.

Managed-WP approaches vulnerabilities like CVE-2025-13766 with urgency, offering actionable fixes, firewall shielding, and continuous monitoring. Prioritize updating MasterStudy LMS, leverage Managed-WP’s protections, and stay vigilant to safeguard your site’s integrity and reputation.

If you require assistance rolling out mitigations or need Managed-WP to apply virtual patches during your upgrade window, contact us to get started immediately at https://my.wp-firewall.com/buy/wp-firewall-free-plan/

---

If desired, Managed-WP can also provide:

• Customized WAF rule sets for immediate Managed-WP dashboard deployment.
• Scripts to audit subscriber-generated posts and media for suspicious content.
• Checklists to guide thorough cleanup and recovery from compromises.

Get in touch with Managed-WP’s security experts for personalized assistance aligned to your website and environment.

---

Take Proactive Action — Secure Your Site with Managed-WP

Don’t risk your business or reputation due to overlooked plugin flaws or weak permissions. Managed-WP provides robust Web Application Firewall (WAF) protection, tailored vulnerability response, and hands-on remediation for WordPress security that goes far beyond standard hosting services.​

Exclusive Offer for Blog Readers: Access our MWPv1r1 protection plan—industry-grade security starting from just USD20/month.

• Automated virtual patching and advanced role-based traffic filtering
• Personalized onboarding and step-by-step site security checklist
• Real-time monitoring, incident alerts, and priority remediation support
• Actionable best-practice guides for secrets management and role hardening

Get Started Easily — Secure Your Site for USD20/month:
Protect My Site with Managed-WP MWPv1r1 Plan

Why trust Managed-WP?

• Immediate coverage against newly discovered plugin and theme vulnerabilities
• Custom WAF rules and instant virtual patching for high-risk scenarios
• Concierge onboarding, expert remediation, and best-practice advice whenever you need it

Don’t wait for the next security breach. Safeguard your WordPress site and reputation with Managed-WP—the choice for businesses serious about security.

Click above to start your protection today (MWPv1r1 plan, USD20/month).