CVE-2026-28343: CKEditor 5 HTML Support Package XSS Vulnerability
Summary
CVE-2026-28343: CKEditor 5 has Cross-site Scripting (XSS) in the HTML Support package. Affects @ckeditor/ckeditor5-html-support versions < 47.6.0. Fixed in 47.6.0. How to fix ↓
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Background
CKEditor 5 is a modern JavaScript rich text editor that provides a wide range of features for content creation and editing. The General HTML Support package allows users to insert HTML content directly into the editor. However, this feature can be misconfigured, leading to security vulnerabilities, particularly Cross-Site Scripting (XSS) attacks.
Vulnerability Detail
A Cross-Site Scripting (XSS) vulnerability has been identified in the General HTML Support feature of CKEditor 5. This vulnerability arises when users can insert specially crafted markup that executes unauthorized JavaScript code. It specifically affects installations where the General HTML Support is enabled and configured to allow unsafe markup, posing a risk of malicious code execution.
How To Fix
Minimum fixed version
47.6.0
This is the first release that contains the fix.
npm install @ckeditor/ckeditor5-html-support@47.6.0Tip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →
Workaround
As a temporary measure, configure the General HTML Support securely to prevent the acceptance of unsafe content. Refer to the Security section of the CKEditor documentation for detailed guidance on how to implement these configurations.
Conclusion
The XSS vulnerability in CKEditor 5's General HTML Support package poses a significant risk if not addressed. It is crucial for users to update to the patched version 47.6.0 or above and to configure their settings securely to prevent exploitation. Utilizing tools like Vulert can help monitor and manage such vulnerabilities effectively.
See every vulnerability recorded for @ckeditor/ckeditor5-html-support →
FAQ
The vulnerability is a Cross-Site Scripting (XSS) issue that allows unauthorized JavaScript execution through unsafe markup in CKEditor 5.
All versions prior to 47.6.0 are affected by this vulnerability.
You can use Vulert, which monitors open-source vulnerabilities in your software. By analyzing your package-lock.json file, it alerts you in real-time. You can also check your application using the Vulert playground without signing up.
If immediate updating is not possible, ensure that your General HTML Support configuration is set to reject unsafe markup to mitigate the risk.
The CVSS score for this vulnerability is 6.4, indicating a moderate severity level.
