CVE-2026-39415: Frappe LMS Auth Bypass Vulnerability

CVE-2026-39415 Overview

A client-side trust vulnerability has been identified in Frappe Learning Management System (LMS), an open-source learning platform designed to help users structure educational content. The vulnerability allows authenticated students to manipulate quiz scores before submission by exploiting improper reliance on client-side calculated scores. This security flaw enables users to alter their quiz results using browser developer tools prior to sending the submission request to the server.

Critical Impact

Authenticated users can modify quiz scores before submission, compromising academic integrity and assessment reliability across the learning platform.

Affected Products

• Frappe Learning Management System (LMS) versions prior to 2.46.0

Discovery Timeline

• 2026-04-08 - CVE-2026-39415 published to NVD
• 2026-04-08 - Last updated in NVD database

Technical Details for CVE-2026-39415

Vulnerability Analysis

This vulnerability falls under CWE-602 (Client-Side Enforcement of Server-Side Security), where the application improperly relies on client-side validation to enforce security controls that should be implemented server-side. The Frappe LMS quiz functionality calculates scores on the client side before transmitting them to the server, creating an opportunity for manipulation.

When a student completes a quiz, the application performs score calculation in the browser using JavaScript. The calculated score is then included in the submission request sent to the backend server. Because the server trusts this client-provided score without performing its own validation or recalculation, an attacker can intercept and modify the score value before the request reaches the server.

While this vulnerability does not allow modification of other users' data or privilege escalation, it fundamentally undermines the integrity of quiz assessments. Educational institutions and organizations relying on Frappe LMS for grading and certification purposes face significant risk to their academic credibility.

Root Cause

The root cause of this vulnerability is the improper trust relationship between the client and server components of the quiz submission system. The application architecture relies on client-side JavaScript to calculate and report quiz scores, without implementing server-side verification. This design flaw violates the fundamental security principle of never trusting client-provided input for critical operations.

The server-side code accepts the score value directly from the submission request without recalculating the actual score based on the student's answers stored in the database. This creates a disconnect between the actual quiz performance and the recorded result.

Attack Vector

The attack is conducted over the network by authenticated users with low privileges (students). The attacker can use browser developer tools to:

1. Complete a quiz normally and receive their actual score
2. Intercept the submission request before it is sent to the server
3. Modify the score parameter in the request payload to any desired value
4. Submit the modified request to record a false score

This manipulation requires no special tools beyond standard browser developer tools, making it accessible to any technically inclined user. The attack does not require any user interaction beyond the attacker's own actions and does not affect the confidentiality of other users' data.

Detection Methods for CVE-2026-39415

Indicators of Compromise

• Unusual patterns in quiz scores such as perfect scores from users with historically poor performance
• Discrepancies between submitted answers and recorded scores when compared manually
• HTTP request logs showing modified score parameters that don't match expected calculation results
• Sudden grade improvements without corresponding improvement in answer quality

Detection Strategies

• Implement logging that captures both client-submitted scores and server-calculated scores for comparison
• Create audit reports that flag statistical anomalies in quiz performance patterns
• Monitor for manipulation attempts by comparing answer selections against submitted scores
• Review web server logs for suspicious modification patterns in quiz submission endpoints

Monitoring Recommendations

• Enable detailed logging of all quiz submission requests including answer data and score values
• Set up alerts for score submissions that exceed statistically normal performance thresholds
• Implement periodic audits comparing submitted answers to recorded grades
• Consider using application performance monitoring tools to track request modification patterns

How to Mitigate CVE-2026-39415

Immediate Actions Required

• Upgrade Frappe Learning Management System to version 2.46.0 or later immediately
• Audit existing quiz records for potential score manipulation by comparing answers to recorded scores
• Implement temporary manual review processes for high-stakes assessments until the patch is applied
• Consider invalidating and requiring retakes for critical assessments submitted during the vulnerable period

Patch Information

The vulnerability is fixed in Frappe LMS version 2.46.0. Organizations should update their installations as soon as possible. The security advisory and patch details are available in the GitHub Security Advisory.

The fix implements proper server-side score calculation, ensuring that quiz scores are computed based on the actual answers stored in the database rather than trusting client-provided values.

Workarounds

• Implement a custom server-side hook to recalculate scores upon submission before storing
• Add manual review requirements for all quiz submissions until the official patch is applied
• Temporarily disable self-graded quizzes for high-stakes assessments
• Use alternative assessment methods such as instructor-graded assignments until the vulnerability is remediated