CVE-2026-81339 Overview
CVE-2026-81339 is an Insecure Direct Object Reference (IDOR) vulnerability in the MasterStudy LMS WordPress Plugin before version 3.7.50. The plugin fails to perform a per-object ownership check when returning quiz attempt results. Any authenticated user holding a minimal subscriber role can read another student's quiz grades, pass/fail status, and attempt timestamps by supplying an attempt identifier that belongs to a different user. The weakness is classified under CWE-639: Authorization Bypass Through User-Controlled Key.
Critical Impact
Low-privilege authenticated users can enumerate and disclose other students' quiz results, exposing academic records and personally attributable performance data across the learning platform.
Affected Products
- MasterStudy LMS WordPress Plugin versions prior to 3.7.50
- WordPress sites running the MasterStudy LMS plugin with subscriber-level registration enabled
- Learning platforms exposing quiz attempt endpoints to authenticated users
Discovery Timeline
- 2026-09-23 - CVE-2026-81339 published to the National Vulnerability Database
- 2026-09-23 - Last updated in the NVD database
Technical Details for CVE-2026-81339
Vulnerability Analysis
The MasterStudy LMS plugin exposes a quiz attempt result endpoint that accepts an attempt identifier as a request parameter. The endpoint validates that the caller is authenticated but does not verify that the caller owns the referenced attempt. Any user with the WordPress subscriber role can request results tied to any other user's attempt identifier.
Because quiz attempt identifiers are sequential integers in typical WordPress database schemas, an attacker can iterate values and harvest grade data for the entire student population. Disclosed data includes numeric grades, pass or fail status, and the timestamp of the attempt. The vulnerability does not require any social engineering or elevated privileges beyond default self-registration.
Root Cause
The root cause is a missing authorization check on a user-controlled key, matching the [CWE-639] pattern. The code path retrieves an attempt record by primary key and returns the result payload without comparing the record's owner to the current session user identifier. Authentication is treated as sufficient authorization, which breaks per-object access boundaries.
Attack Vector
Exploitation proceeds over the network against the WordPress REST or admin-ajax interface exposed by the plugin. The attacker registers a subscriber account, authenticates, and issues requests that reference attempt identifiers belonging to other students. No user interaction from the victim is required. The impact is limited to confidentiality of quiz result data; integrity and availability are not affected.
Refer to the WPScan Vulnerability Report for endpoint-specific technical details.
Detection Methods for CVE-2026-81339
Indicators of Compromise
- Repeated authenticated requests to MasterStudy LMS quiz result endpoints that iterate a numeric attempt identifier parameter
- Subscriber-role accounts issuing high volumes of quiz-related API calls without matching quiz submission activity
- Access log entries where the requesting user identifier does not match the owner of the requested attempt record
Detection Strategies
- Instrument the plugin's quiz result handler to log the requesting user identifier alongside the owner of the returned attempt, then alert on mismatches
- Baseline normal quiz result request rates per subscriber and flag accounts that exceed typical read volumes
- Correlate newly registered subscriber accounts with immediate access to bulk quiz result endpoints
Monitoring Recommendations
- Forward WordPress access logs and plugin audit trails to a centralized log platform for retention and correlation
- Monitor for sequential-integer scanning patterns against /wp-json/ and admin-ajax.php endpoints tied to MasterStudy LMS
- Track privilege distribution and creation cadence of subscriber accounts to detect abuse-oriented registration surges
How to Mitigate CVE-2026-81339
Immediate Actions Required
- Upgrade the MasterStudy LMS WordPress Plugin to version 3.7.50 or later on every affected site
- Audit recent access logs for authenticated calls to quiz result endpoints and identify subscriber accounts issuing anomalous requests
- Review WordPress registration settings and disable open subscriber registration where it is not required
Patch Information
The vendor addressed the issue in MasterStudy LMS WordPress Plugin version 3.7.50 by enforcing a per-object ownership check before returning quiz attempt results. Site administrators should apply the update through the WordPress plugin manager or by deploying the updated plugin package. See the WPScan Vulnerability Report for release references.
Workarounds
- Temporarily restrict access to the vulnerable quiz result endpoint at the web server or WAF layer until patching is complete
- Disable self-service subscriber registration to reduce the pool of accounts that can exercise the flaw
- Rotate or invalidate suspicious subscriber accounts identified during log review
# Example WordPress CLI upgrade command
wp plugin update masterstudy-lms-learning-management-system --version=3.7.50
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
