CVE-2026-23497: Frappe Learning XSS Vulnerability

CVE-2026-23497 Overview

A stored Cross-Site Scripting (XSS) vulnerability has been identified in Frappe Learning Management System (LMS), a learning platform designed to help organizations structure and deliver educational content. The vulnerability exists in versions 2.44.0 and earlier, where a specially crafted image filename can execute malicious JavaScript code when rendered on course or jobs pages.

This vulnerability allows attackers to inject persistent malicious scripts into the application by uploading files with carefully crafted filenames containing JavaScript payloads. When other users browse to pages where these filenames are displayed, the malicious code executes in their browser context.

Critical Impact

Attackers can execute arbitrary JavaScript in victim browsers, potentially leading to session hijacking, credential theft, defacement of course content, or phishing attacks targeting LMS users.

Affected Products

• Frappe Learning Management System versions 2.44.0 and earlier
• All deployments using the vulnerable file upload functionality on course pages
• All deployments using the vulnerable file upload functionality on jobs pages

Discovery Timeline

• 2026-01-14 - CVE CVE-2026-23497 published to NVD
• 2026-01-16 - Last updated in NVD database

Technical Details for CVE-2026-23497

Vulnerability Analysis

The vulnerability is classified under CWE-79 (Improper Neutralization of Input During Web Page Generation), commonly known as Cross-Site Scripting. This stored XSS flaw occurs because the Frappe LMS application fails to properly sanitize or encode image filenames before rendering them in HTML output on course and jobs pages.

When a user uploads an image with a malicious filename containing JavaScript code, the application stores this filename as-is in the database. Subsequently, when the application generates HTML to display these images to users, the unsanitized filename is embedded directly into the page content. If the filename contains executable script tags or event handlers, the browser interprets and executes this code in the context of the authenticated user's session.

The network-based attack vector means that exploitation can be performed remotely by any authenticated user with file upload privileges. User interaction is required, as victims must navigate to a page where the malicious filename is rendered.

Root Cause

The root cause of this vulnerability is insufficient input validation and output encoding in the file upload handling mechanism. Specifically, the application fails to sanitize image filenames upon upload and does not properly encode these filenames when rendering them in HTML templates. This allows specially crafted filenames containing HTML or JavaScript to be interpreted as executable code rather than plain text when displayed in the browser.

Attack Vector

The attack is executed via the network through the web interface. An attacker with access to upload images (such as a course instructor or job poster) can craft a filename containing malicious JavaScript payload. Common attack patterns include embedding script tags or event handlers within the filename string.

When this file is uploaded and stored, any user who subsequently views the course page or jobs page where the filename is displayed will have the malicious script executed in their browser. This can lead to session token theft, unauthorized actions performed on behalf of the victim, or redirection to attacker-controlled phishing sites.

The vulnerability does not require complex exploitation techniques—attackers simply need to manipulate the filename of an image file before uploading it through the standard upload functionality.

Detection Methods for CVE-2026-23497

Indicators of Compromise

• Presence of image files with filenames containing HTML tags such as <script>, <img onerror=, or similar JavaScript event handlers
• Database entries in file or image tables containing suspicious characters or encoded JavaScript payloads
• User reports of unexpected browser behavior or pop-ups when viewing course or jobs pages
• Web application firewall logs showing attempts to upload files with script-like patterns in filenames

Detection Strategies

• Implement web application firewall rules to detect and block file uploads containing script tags or JavaScript event handlers in filenames
• Deploy endpoint detection solutions like SentinelOne to identify suspicious browser activity or script execution patterns
• Enable detailed logging on file upload endpoints and monitor for anomalous filename patterns
• Conduct periodic security scans of the database to identify stored XSS payloads in filename fields

Monitoring Recommendations

• Monitor web server access logs for requests to course and jobs pages that coincide with reports of unusual client-side behavior
• Configure alerting for file uploads where filenames exceed typical length or contain special characters commonly used in XSS attacks
• Review Content Security Policy violation reports if CSP is implemented, as these may indicate attempted XSS execution
• Track user session anomalies that may suggest session hijacking resulting from successful XSS exploitation

How to Mitigate CVE-2026-23497

Immediate Actions Required

• Upgrade Frappe LMS to a patched version that addresses this vulnerability
• Audit existing uploaded files in the database for malicious filename patterns and sanitize or remove any suspicious entries
• Implement Content Security Policy headers to restrict inline script execution as a defense-in-depth measure
• Consider temporarily restricting file upload capabilities to trusted users until the patch is applied

Patch Information

Frappe has released a security patch addressing this vulnerability. The fix is available in commit e7ccf0a711d0e0ab5e6b28b7a1e4e0510b6b9543. Organizations should update their Frappe LMS installations to incorporate this fix. For detailed information about the vulnerability and the patch, refer to the GitHub Security Advisory and the GitHub commit containing the fix.

Workarounds

• Implement server-side filename sanitization to strip or encode special characters before storing uploaded files
• Deploy a web application firewall with rules to block file uploads containing potentially malicious filename patterns
• Enable strict Content Security Policy headers to prevent execution of inline scripts as a mitigating control
• Restrict file upload permissions to only trusted administrative users until the official patch can be applied

# Example Content Security Policy header configuration for nginx
add_header Content-Security-Policy "default-src 'self'; script-src 'self'; object-src 'none';" always;