Preventing Cross-Site Scripting (XSS)

5 Mar 20259 minutes to read

The Rich Text Editor allows users to edit the content with security by preventing cross-site scripting (XSS). By default, it provides built-in support to remove elements from editor content that cause XSS attacks. The editor removes the elements based on the attributes if it is possible to execute a script.

The enableHtmlSanitize property determines whether XSS prevention is active. It’s set to true by default.

In the following sample, we removed the script tag and onmouseover attribute from the content of the Rich Text Editor.

index.js
index.html
/**
 * Prevention of XSS attack sample
 */
var rteValue = `<div onmouseover='javascript:alert(1)'>Prevention of Cross Sit Scripting (XSS) </div> <script>alert('hi')</script>`;

var defaultRTE = new ej.richtexteditor.RichTextEditor({
   value: rteValue
});
defaultRTE.appendTo("#defaultRTE");
<!DOCTYPE html><html lang="en"><head>
    <title>Essential JS 2 Rich Text Editor</title>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta name="description" content="Typescript UI Controls">
    <meta name="author" content="Syncfusion">
    <link href="index.css" rel="stylesheet">
    <link href="https://cdn.syncfusion.com/ej2/29.1.33/ej2-base/styles/material.css" rel="stylesheet">
    <link href="https://cdn.syncfusion.com/ej2/29.1.33/ej2-richtexteditor/styles/material.css" rel="stylesheet">
    <link href="https://cdn.syncfusion.com/ej2/29.1.33/ej2-inputs/styles/material.css" rel="stylesheet">
    <link href="https://cdn.syncfusion.com/ej2/29.1.33/ej2-lists/styles/material.css" rel="stylesheet">
    <link href="https://cdn.syncfusion.com/ej2/29.1.33/ej2-navigations/styles/material.css" rel="stylesheet">
    <link href="https://cdn.syncfusion.com/ej2/29.1.33/ej2-popups/styles/material.css" rel="stylesheet">
     <link href="https://cdn.syncfusion.com/ej2/29.1.33/ej2-buttons/styles/material.css" rel="stylesheet">
    <link href="https://cdn.syncfusion.com/ej2/29.1.33/ej2-splitbuttons/styles/material.css" rel="stylesheet">
    
    
<script src="https://cdn.syncfusion.com/ej2/29.1.33/dist/ej2.min.js" type="text/javascript"></script>
<script src="https://cdn.syncfusion.com/ej2/syncfusion-helper.js" type ="text/javascript"></script>
</head>

<body>
    
    <div id="container">
        <div id="defaultRTE">
        </div>
    </div>


<script>
var ele = document.getElementById('container');
if(ele) {
  ele.style.visibility = "visible";
}   
      </script>
<script src="index.js" type="text/javascript"></script>
</body></html>

The XSS prevention feature is only applicable when the editorMode is set to HTML.

Custom Cross-Site Scripting Prevention

For more precise control over XSS prevention, you can implement custom filtering logic using the beforeSanitizeHtml event.

Implementing Custom Cross-Site Scripting and Fililtering in Rich Text Editor

Use the beforeSanitizeHtml event to define custom filtering rules.
Utilize the helper function from the event argument to apply your custom filters.
Set the cancel argument to true if you want to override the built-in XSS prevention entirely.

The following sample demonstrates how to filter the script tag by value.

index.js
index.html
/**
 * Custom cross-site scripting sample
 */
var rteValue = `<div>Prevention of Cross Sit Scripting (XSS) </div> <script>alert('hi')</script>`;

var defaultRTE = new ej.richtexteditor.RichTextEditor({
  value: rteValue,
  beforeSanitizeHtml: (e) => {
    e.helper = (value) => {
      e.cancel = true;
      var temp = document.createElement('div');
      temp.innerHTML = value;
      var scriptTag = temp.querySelector('script');
      if (scriptTag) {
        ej.base.detach(scriptTag);
      }
      return temp.innerHTML;
    }
  }
});
defaultRTE.appendTo('#defaultRTE');
<!DOCTYPE html><html lang="en"><head>
    <title>Essential JS 2 Rich Text Editor</title>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta name="description" content="Typescript UI Controls">
    <meta name="author" content="Syncfusion">
    <link href="index.css" rel="stylesheet">
    <link href="https://cdn.syncfusion.com/ej2/29.1.33/ej2-base/styles/material.css" rel="stylesheet">
    <link href="https://cdn.syncfusion.com/ej2/29.1.33/ej2-richtexteditor/styles/material.css" rel="stylesheet">
    <link href="https://cdn.syncfusion.com/ej2/29.1.33/ej2-inputs/styles/material.css" rel="stylesheet">
    <link href="https://cdn.syncfusion.com/ej2/29.1.33/ej2-lists/styles/material.css" rel="stylesheet">
    <link href="https://cdn.syncfusion.com/ej2/29.1.33/ej2-navigations/styles/material.css" rel="stylesheet">
    <link href="https://cdn.syncfusion.com/ej2/29.1.33/ej2-popups/styles/material.css" rel="stylesheet">
     <link href="https://cdn.syncfusion.com/ej2/29.1.33/ej2-buttons/styles/material.css" rel="stylesheet">
    <link href="https://cdn.syncfusion.com/ej2/29.1.33/ej2-splitbuttons/styles/material.css" rel="stylesheet">
    
    
<script src="https://cdn.syncfusion.com/ej2/29.1.33/dist/ej2.min.js" type="text/javascript"></script>
<script src="https://cdn.syncfusion.com/ej2/syncfusion-helper.js" type ="text/javascript"></script>
</head>

<body>
    
    <div id="container">
        <div id="defaultRTE">
        </div>
    </div>


<script>
var ele = document.getElementById('container');
if(ele) {
  ele.style.visibility = "visible";
}   
      </script>
<script src="index.js" type="text/javascript"></script>
</body></html>

You can also filter out the e.selectors.tags and e.selector.attributs in the beforeSanitizeHtml event to control which HTML tags and attributes are allowed to appear.

For instance, if you want to display <iframe>, By manipulating the e.selectors.tags property in this event, you can selectively remove tags like <iframe>. This approach ensures that your application can safely display iframes while preventing potential security risks associated with XSS vulnerabilities.

The following sample demonstrates how to filter the iframe tag.

index.js
index.html
var rteValue = `<div>Prevention of Cross Sit Scripting (XSS) </div> <script>alert('hi')</script>`;

var defaultRTE = new ej.richtexteditor.RichTextEditor({
  value: rteValue,
  beforeSanitizeHtml: (e) => {
    if (e.selectors && e.selectors.tags) {
      e.selectors.tags = e.selectors.tags.filter((tag) => tag !== 'iframe:not(.e-rte-embed-url)');
      e.selectors.tags = [('iframe[src^="https://"]')];
    }
  }
});
defaultRTE.appendTo('#defaultRTE');
<!DOCTYPE html><html lang="en"><head>
    <title>Essential JS 2 Rich Text Editor</title>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta name="description" content="Typescript UI Controls">
    <meta name="author" content="Syncfusion">
    <link href="index.css" rel="stylesheet">
    <link href="https://cdn.syncfusion.com/ej2/29.1.33/ej2-base/styles/material.css" rel="stylesheet">
    <link href="https://cdn.syncfusion.com/ej2/29.1.33/ej2-richtexteditor/styles/material.css" rel="stylesheet">
    <link href="https://cdn.syncfusion.com/ej2/29.1.33/ej2-inputs/styles/material.css" rel="stylesheet">
    <link href="https://cdn.syncfusion.com/ej2/29.1.33/ej2-lists/styles/material.css" rel="stylesheet">
    <link href="https://cdn.syncfusion.com/ej2/29.1.33/ej2-navigations/styles/material.css" rel="stylesheet">
    <link href="https://cdn.syncfusion.com/ej2/29.1.33/ej2-popups/styles/material.css" rel="stylesheet">
     <link href="https://cdn.syncfusion.com/ej2/29.1.33/ej2-buttons/styles/material.css" rel="stylesheet">
    <link href="https://cdn.syncfusion.com/ej2/29.1.33/ej2-splitbuttons/styles/material.css" rel="stylesheet">
    
    
<script src="https://cdn.syncfusion.com/ej2/29.1.33/dist/ej2.min.js" type="text/javascript"></script>
<script src="https://cdn.syncfusion.com/ej2/syncfusion-helper.js" type ="text/javascript"></script>
</head>

<body>
    
    <div id="container">
        <div id="defaultRTE">
        </div>
    </div>


<script>
var ele = document.getElementById('container');
if(ele) {
  ele.style.visibility = "visible";
}   
      </script>
<script src="index.js" type="text/javascript"></script>
</body></html>