CVE-2021-42228: Kindsoft KindEditor CSRF Vulnerability

CVE-2021-42228 Overview

A Cross Site Request Forgery (CSRF) vulnerability exists in KindEditor 4.1.x, as demonstrated by examples/uploadbutton.html. This vulnerability allows attackers to trick authenticated users into performing unintended actions on the KindEditor application by crafting malicious web pages or links. When a victim with an active session visits a malicious site, the attacker can execute unauthorized operations on behalf of the user without their knowledge or consent.

Critical Impact

Attackers can leverage this CSRF vulnerability to perform unauthorized actions such as file uploads, content modifications, or configuration changes in KindEditor by exploiting the lack of anti-CSRF token validation in affected endpoints.

Affected Products

• KindSoft KindEditor 4.1.x versions
• Applications integrating KindEditor 4.1.x with exposed example files
• Web platforms utilizing the vulnerable uploadbutton.html example component

Discovery Timeline

• 2021-10-14 - CVE-2021-42228 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-42228

Vulnerability Analysis

This Cross Site Request Forgery (CSRF) vulnerability (CWE-352) exists in the KindEditor rich text editor, specifically within the example files shipped with version 4.1.x. The vulnerable component examples/uploadbutton.html does not implement proper anti-CSRF protections, allowing attackers to forge requests that appear legitimate to the server.

When a user is authenticated to an application using KindEditor and visits a malicious webpage crafted by an attacker, the browser automatically includes session cookies with any request to the KindEditor application. Since the upload functionality lacks CSRF token validation, the server cannot distinguish between legitimate user-initiated requests and forged requests from malicious sites.

Root Cause

The root cause of this vulnerability is the absence of CSRF token validation in the examples/uploadbutton.html file and related upload functionality. The KindEditor application fails to implement proper state-changing request verification mechanisms such as:

• Synchronizer tokens (CSRF tokens) that validate request authenticity
• Same-origin validation through custom headers
• Double-submit cookie patterns

This oversight allows cross-origin requests to be processed as legitimate actions when the victim has an active authenticated session.

Attack Vector

The attack vector is network-based and requires user interaction. An attacker must craft a malicious webpage containing a hidden form or JavaScript that targets the vulnerable KindEditor endpoint. The attack sequence involves:

1. Attacker identifies a target application using KindEditor 4.1.x with exposed example files
2. Attacker creates a malicious webpage with a hidden form targeting the vulnerable upload endpoint
3. Victim with an active session on the target application visits the attacker's page
4. The malicious page automatically submits a forged request to the KindEditor endpoint
5. The victim's browser includes authentication cookies, causing the server to process the unauthorized action

The vulnerability is triggered through the examples/uploadbutton.html endpoint, which processes file upload requests without verifying the request origin or validating anti-CSRF tokens. Attackers can host a webpage that automatically submits forms or sends AJAX requests to the vulnerable endpoint when visited by an authenticated user.

Detection Methods for CVE-2021-42228

Indicators of Compromise

• Unusual file uploads originating from unexpected referrer headers or lacking referrer information
• Authentication sessions showing activity from multiple geographic locations or IP addresses in short timeframes
• Web server logs revealing requests to examples/uploadbutton.html with suspicious or external referrer domains
• Unexpected content modifications or file uploads that users do not recall performing

Detection Strategies

• Implement web application firewall (WAF) rules to detect and block requests with missing or invalid CSRF tokens
• Monitor HTTP referrer headers for requests to sensitive KindEditor endpoints and flag external origins
• Deploy anomaly detection to identify unusual patterns in file upload behavior or content modifications
• Review access logs for requests to example files that should not be accessible in production environments

Monitoring Recommendations

• Enable detailed logging for all KindEditor upload endpoints and review logs for suspicious activity patterns
• Configure alerting for requests originating from external referrers to sensitive application endpoints
• Implement session monitoring to detect concurrent access from multiple locations or unusual user agent patterns
• Regularly audit web server configurations to ensure example and demo files are not exposed in production

How to Mitigate CVE-2021-42228

Immediate Actions Required

• Remove or restrict access to example files including examples/uploadbutton.html from production deployments
• Implement CSRF token validation on all state-changing endpoints in applications using KindEditor
• Configure web server rules to block access to the /examples/ directory
• Review recent logs for evidence of exploitation and investigate any suspicious upload activity

Patch Information

As of the last NVD update on 2024-11-21, users should check the GitHub Issue Report for the latest status on official fixes from KindSoft. Organizations should monitor the KindEditor repository for security updates and consider implementing custom CSRF protections if official patches are not available.

Workarounds

• Delete or rename the examples directory from KindEditor installations to prevent access to vulnerable components
• Implement server-side CSRF token validation by adding token generation and verification to all form submissions
• Configure web server access controls to deny requests to example files and directories
• Use Content Security Policy (CSP) headers to restrict form submission targets and mitigate cross-origin attack vectors
• Consider migrating to actively maintained rich text editor alternatives with built-in CSRF protections

# Configuration example - Apache .htaccess to block access to examples directory
<Directory "/path/to/kindeditor/examples">
    Order deny,allow
    Deny from all
</Directory>

# Nginx configuration to block examples directory
location /kindeditor/examples {
    deny all;
    return 403;
}