CVE-2026-57330 Overview
CVE-2026-57330 is a stored Cross-Site Scripting (XSS) vulnerability affecting the MasterStudy LMS WordPress plugin in versions up to and including 3.7.27. The flaw allows authenticated users with subscriber-level privileges to inject malicious JavaScript into the application. The injected payload executes in the browser of any user who views the affected content, including administrators. The issue is categorized under [CWE-79] Improper Neutralization of Input During Web Page Generation. Successful exploitation can lead to session theft, account takeover, and further compromise of the WordPress site.
Critical Impact
An attacker with a low-privilege subscriber account can inject stored JavaScript that executes in the context of higher-privileged users, enabling session hijacking and privileged action abuse.
Affected Products
- MasterStudy LMS Learning Management System WordPress plugin
- Versions <= 3.7.27
- WordPress sites using the vulnerable plugin build
Discovery Timeline
- 2026-06-29 - CVE-2026-57330 published to NVD
- 2026-06-29 - Last updated in NVD database
Technical Details for CVE-2026-57330
Vulnerability Analysis
The vulnerability resides in input handling paths within MasterStudy LMS that are accessible to authenticated subscribers. User-supplied content is stored and later rendered without sufficient output encoding or input sanitization. When the rendered page is loaded by another user, the browser interprets injected <script> payloads as executable code. Because the plugin is a learning management system, subscriber accounts are often granted by default through open registration, expanding the pool of potential attackers. The CVSS vector indicates that the attack crosses a security scope boundary, meaning the impact extends beyond the initially compromised component to other users of the WordPress site.
Root Cause
The root cause is missing or insufficient output escaping of subscriber-controlled fields before rendering them into HTML contexts. The plugin fails to apply WordPress sanitization primitives such as esc_html(), esc_attr(), or wp_kses() to input before storage or during output. Refer to the Patchstack XSS Vulnerability Advisory for detailed vendor and disclosure information.
Attack Vector
Exploitation requires an authenticated subscriber account and user interaction from a victim who views the injected content. The attacker submits a crafted payload containing JavaScript through a plugin field accessible to subscribers. When an administrator or instructor loads the page rendering that field, the payload executes with their session context. This enables actions such as exfiltrating cookies, issuing authenticated requests, or modifying site configuration through the WordPress REST API.
No verified public exploit code is available. The vulnerability mechanism follows standard stored XSS patterns in WordPress plugins where unsanitized user input is echoed into HTML output.
Detection Methods for CVE-2026-57330
Indicators of Compromise
- Unexpected <script>, onerror=, or onload= strings stored in MasterStudy LMS database tables or post metadata.
- Administrator sessions exhibiting unusual outbound requests to attacker-controlled domains after viewing LMS content.
- New administrator accounts or role changes created shortly after LMS pages were accessed.
- Subscriber accounts registered from anonymizing infrastructure that immediately submit content to LMS endpoints.
Detection Strategies
- Review WordPress wp_posts, wp_postmeta, and MasterStudy-specific tables for HTML event handlers or script tags in subscriber-authored fields.
- Monitor web server access logs for POST requests to MasterStudy LMS endpoints from low-privilege accounts followed by admin page renders.
- Enable a Content Security Policy (CSP) in report-only mode to surface unexpected inline script execution on LMS pages.
Monitoring Recommendations
- Audit new subscriber registrations and correlate account creation with immediate content submissions.
- Alert on WordPress REST API calls to privileged endpoints originating from browser sessions that recently loaded LMS instructor pages.
- Track administrator role assignments and plugin/theme modifications for unauthorized changes.
How to Mitigate CVE-2026-57330
Immediate Actions Required
- Update MasterStudy LMS to a version later than 3.7.27 as soon as the vendor patch is available.
- Disable open user registration on WordPress sites where subscriber accounts are not operationally required.
- Audit existing subscriber-submitted content for stored script payloads and remove suspicious entries.
- Rotate administrator credentials and invalidate active sessions if compromise is suspected.
Patch Information
Refer to the Patchstack XSS Vulnerability Advisory for the fixed version and vendor remediation guidance. Apply the patched release through the WordPress plugin updater or via manual replacement of the plugin directory.
Workarounds
- Restrict subscriber registration and require manual approval of new accounts until the plugin is patched.
- Deploy a Web Application Firewall (WAF) rule that blocks HTML tags and JavaScript event handlers in requests targeting MasterStudy LMS endpoints.
- Enforce a strict Content Security Policy that disallows inline scripts on WordPress admin and LMS pages.
- Limit access to LMS administrative views to accounts using hardware-backed multi-factor authentication.
# Example WordPress CLI commands to inventory and update the plugin
wp plugin list --name=masterstudy-lms-learning-management-system --fields=name,status,version
wp plugin update masterstudy-lms-learning-management-system
wp user list --role=subscriber --fields=ID,user_login,user_registered
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
