I’m working on an MVC application and need to ensure that users cannot input any harmful JavaScript code into a TinyMCE rich text editor. Currently, I’m using a regular expression for validation; however, I overlooked the fact that the rich text editor generates its own HTML, causing the regex to fail. Here’s the regex I’ve been utilizing:
[RegularExpression("^[a-zA-Z0-9\s-'\.]+$", ErrorMessage = "Only letters, numbers, spaces, and '-' are permitted in the description.")]
Despite my efforts to mitigate this issue by changing the settings to allow specific elements, I still found that users could insert script tags. The code I used is as follows:
valid_elements : "a[href|target=_blank],strong/b,div[align],br",
Could anyone suggest a better approach to enforce this restriction?
Consider using TinyMCE's content_security_policy option for better control over scripts.
Here's a quick example:
tinymce.init({
selector: 'textarea',
content_security_policy: "default-src 'self'; script-src 'none';"
});
This policy blocks all JavaScript execution within the editor content. It's more robust than regex for preventing script injections.
Additionally, validate on the server-side to ensure no harmful scripts are processed.
Beyond regex validation, harnessing TinyMCE's configurations can effectively prevent JavaScript injections. Here’s an optimized approach to address this challenge:
- Use the
invalid_elements Setting: Explicitly block undesirable elements like <script>. This reduces the risk of malicious input.
tinymce.init({
selector: 'textarea',
invalid_elements: 'script,iframe'
});
- Extend Server-side Validation: Ensure your server-side logic further sanitizes and reviews input. Utilize libraries like DOMPurify to strip harmful content while retaining essential formatting.
const DOMPurify = require('dompurify');
const cleanHTML = DOMPurify.sanitize(userInput);
- Double-check the Output: Finally, verify the content right before rendering on the client to catch anything slipped through earlier checks.
By integrating these methods, you create a robust defense against script injections while maintaining usability. This setup emphasizes performance and reliability without adding much complexity.
To further strengthen your defense against JavaScript input in TinyMCE, leveraging a combination of both client-side configuration and rigorous server-side sanitization can be highly effective. Here’s an alternative approach:
- Customize with the
extended_valid_elements Option: Define the specific elements and attributes that are allowed. You can limit the attributes to only those absolutely necessary for your use case.
tinymce.init({
selector: 'textarea',
extended_valid_elements: 'a[href|title],strong,em',
// more configurations...
});
- Implement Content Filtering Plugins: Consider using plugins like XSS for advanced Input filtering on the server-side, which provides a strong layer of security against XSS attacks by removing potentially dangerous elements and attributes.
const xss = require('xss');
const cleanInput = xss(userInput, {
whiteList: {}, // empty means only text allowed
stripIgnoreTag: true // filter out all html not in the whitelist
});
- Use a Secure Content Delivery Network (CDN): When serving TinyMCE or related scripts, use secure CDNs that enforce HTTPS and offer additional security features like Subresource Integrity (SRI) to ensure scripts have not been tampered with during delivery.
<script src="https://cdn.tiny.cloud/1/your-api-key/tinymce/5/tinymce.min.js" integrity="sha384-LtWl0ykYke6G0M3R+kRcl9NUEwBQ6NI3nTjIsb3DnGo1oh9sv/4v3lH85JA03Q3z" crossorigin="anonymous"></script>
By enforcing these best practices, you improve your application's resistance against script-based attacks while still allowing legitimate content generation. This method complements other techniques previously mentioned, providing a comprehensive approach to security within TinyMCE.