CVE-2022-23494: Tiny Tinymce XSS Vulnerability

CVE-2022-23494 Overview

CVE-2022-23494 is a Cross-Site Scripting (XSS) vulnerability discovered in TinyMCE, a widely-used open source rich text editor. The vulnerability exists in the alert and confirm dialogs when these dialogs are provided with malicious HTML content. This can occur in plugins that use the alert or confirm dialogs, such as in the image plugin, which presents these dialogs when certain errors occur. The vulnerability allowed arbitrary JavaScript execution when an alert was presented in the TinyMCE UI for the current user.

Critical Impact

Arbitrary JavaScript execution in the context of the user's browser session when malicious HTML content is rendered in TinyMCE alert or confirm dialogs, potentially leading to session hijacking, data theft, or unauthorized actions.

Affected Products

• TinyMCE versions prior to 5.10.7
• TinyMCE versions 6.x prior to 6.3.1
• Applications integrating vulnerable TinyMCE versions with image upload functionality

Discovery Timeline

• 2022-12-08 - CVE-2022-23494 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-23494

Vulnerability Analysis

This Cross-Site Scripting (XSS) vulnerability stems from improper HTML sanitization in TinyMCE's dialog components. The alert and confirm dialogs failed to properly sanitize HTML content after unwrapping invalid elements, allowing malicious scripts to execute within the editor's context.

The vulnerability is particularly concerning because it affects the image plugin, which is commonly used in content management systems and web applications. When certain error conditions occur during image upload operations, the plugin displays error messages through these vulnerable dialogs. An attacker who can control the error messages or inject malicious content into the upload handler response can trigger JavaScript execution in the victim's browser.

The attack requires user interaction (the user must trigger the dialog display), and successful exploitation could result in confidentiality and integrity impacts through unauthorized access to user session data or manipulation of editor content.

Root Cause

The root cause of this vulnerability is insufficient HTML sanitization when rendering content in TinyMCE's alert and confirm dialog components. Specifically, the dialogs were not performing HTML sanitization after unwrapping invalid elements, creating a gap where malicious JavaScript could be injected and executed.

The vulnerable code path allowed unsanitized HTML to be rendered directly in the dialog UI, bypassing the expected security controls. This is classified as CWE-79 (Improper Neutralization of Input During Web Page Generation).

Attack Vector

The attack vector for CVE-2022-23494 is network-based, requiring user interaction to trigger the vulnerable dialog. An attacker could exploit this vulnerability by:

1. Crafting a malicious images_upload_handler response containing XSS payloads
2. Manipulating error messages displayed by the image plugin
3. Injecting malicious HTML content that triggers the vulnerable alert or confirm dialogs

When a user interacts with the TinyMCE editor and encounters an error condition that displays a dialog with the malicious content, the embedded JavaScript executes in the user's browser context.

The security patch introduces proper HTML sanitization using the DOMPurify library:

// Security patch: HtmlSanitizer.ts
// Source: https://github.com/tinymce/tinymce/commit/6923d85eba6de3e08ebc9c5a387b5abdaa21150e

import createDompurify from 'dompurify';

export const sanitizeHtmlString = (html: string): string => createDompurify().sanitize(html);

The fix also integrates the sanitizer into the dialog rendering pipeline:

// Security patch: Dialogs.ts
// Source: https://github.com/tinymce/tinymce/commit/6923d85eba6de3e08ebc9c5a387b5abdaa21150e

import Env from 'tinymce/core/api/Env';

import { UiFactoryBackstageProviders } from '../../backstage/Backstage';
import * as HtmlSanitizer from '../core/HtmlSanitizer';
import * as NavigableObject from '../general/NavigableObject';

const isTouch = Env.deviceType.isTouch();

Detection Methods for CVE-2022-23494

Indicators of Compromise

• Unusual JavaScript execution or network requests originating from TinyMCE editor contexts
• Suspicious error messages containing script tags or event handlers in TinyMCE dialogs
• Unexpected modifications to editor content or user session behavior
• Browser console errors related to Content Security Policy violations in TinyMCE components

Detection Strategies

• Implement Content Security Policy (CSP) headers to detect and block unauthorized script execution
• Monitor web application logs for unusual patterns in image upload handler responses
• Perform static code analysis to identify applications using vulnerable TinyMCE versions
• Use Software Composition Analysis (SCA) tools to identify vulnerable TinyMCE dependencies in your codebase

Monitoring Recommendations

• Enable browser developer tools to monitor for unexpected script execution in TinyMCE contexts
• Implement logging on images_upload_handler responses to detect potential injection attempts
• Monitor for anomalous user session activity following TinyMCE editor interactions
• Set up alerts for JavaScript errors originating from TinyMCE dialog components

How to Mitigate CVE-2022-23494

Immediate Actions Required

• Upgrade TinyMCE to version 5.10.7 or later for the 5.x branch
• Upgrade TinyMCE to version 6.3.1 or later for the 6.x branch
• Review and audit all custom images_upload_handler implementations for proper input validation
• Implement Content Security Policy headers to provide defense-in-depth against XSS attacks

Patch Information

The vulnerability has been patched in TinyMCE 5.10.7 and TinyMCE 6.3.1 by ensuring HTML sanitization was still performed after unwrapping invalid elements. The fix integrates the DOMPurify library to sanitize all HTML content before rendering in alert and confirm dialogs.

Patch commits are available:

• Patch for TinyMCE 6.x branch
• Patch for TinyMCE 5.x branch

For detailed release notes, see:

• TinyMCE 5.10.7 Release Notes
• TinyMCE 6.3 Release Notes

Workarounds

• Ensure the images_upload_handler returns a valid value as per the images_upload_handler documentation
• Implement server-side validation of all content passed to TinyMCE dialogs
• Consider disabling the image plugin if image upload functionality is not required
• Apply strict Content Security Policy headers to prevent inline script execution

# Example: Upgrade TinyMCE via npm
npm update tinymce@5.10.7  # For 5.x branch
npm update tinymce@6.3.1   # For 6.x branch

# Verify installed version
npm list tinymce