XSS within RadEditor

Progress® Telerik® UI for ASP.NET AJAX Feedback Portal

Create an account Log In

Back to Feed

Request a Feature Report a Bug

Unplanned

Last Updated: 01 Feb 2022 09:23 by ADMIN

Andrew

Created on: 17 Dec 2021 03:13

Category: Editor

Type: Bug Report

XSS within RadEditor

Hi,

I am contacting you today to let you know I have found cross-site scripting vectors within the latest version of the RadEditor. I have attached images of the payloads that seem to bypass the XSS filter.

The second payload only works on Firefox browsers, but the first works on Chrome browsers too. While it still requires users to click on the link to trigger XSS, it can be easily social engineered in most situations.

3 comments

ADMIN

Peter Milchev

Posted on: 01 Feb 2022 09:23

Hi Sullivanst,

Thank you for pointing this out, the old check indeed had this flaw. I have updated the code so it first makes the attribute lower case and then searches with indexOf:

 if (attr && attr.toLowerCase().indexOf("javascript") > -1) {

Regards,
Peter Milchev
Progress Telerik

Virtual Classroom, the free self-paced technical training that gets you up to speed with Telerik and Kendo UI products quickly just got a fresh new look + new and improved content including a brand new Blazor course! Check it out at https://learn.telerik.com/.

Matthew

Posted on: 31 Jan 2022 21:46

Looks like it's an issue with the suggested remediation that it's case sensitive, whereas the URL scheme is not. I'll be modifying my implementation to also reject "JAVASCRIPT:" urls ;)

ADMIN

Peter Milchev

Posted on: 23 Dec 2021 14:53

Hello Andrew,

Thank you for bringing up this case, it indeed is not sanitized by the DOM or events sanitizers. The same issue is observed also with the <animate> tag in the SVG as well:

For the time being, you can alleviate the issue by using a custom filter client-side and manually sanitizing the content on the server-side:

https://docs.telerik.com/devtools/aspnet-ajax/controls/editor/managing-content/prevent-cross-site-scripting-(xss)

Here is a sample implementation of the client-side filter:

<script type="text/javascript">
    function OnClientLoad(editor, args) {
        editor.get_filtersManager().add(new MyCustomSVGFilter());
    }

    function MyCustomSVGFilter() {
        MyCustomSVGFilter.initializeBase(this);
        this.set_isDom(true);
        this.set_enabled(true);
        this.set_name("MyCustomSVGFilter");
        this.set_description("Strips set, animate and brute attributes that contain 'javascript:' as value");
    }

    MyCustomSVGFilter.prototype = {
        encodeScripts: function (contentToEncode) {
            var list = contentToEncode.getElementsByTagName("set");
            for (let item of list) {
                var attr = item.getAttribute("to");
                if (attr && attr.toLowerCase().indexOf("javascript") > -1) {
                    item.removeAttribute("to");
                }
            }
            list = contentToEncode.getElementsByTagName("animate");
            for (let item of list) {
                var attr = item.getAttribute("to");
                if (attr && attr.toLowerCase().indexOf("javascript") > -1) {
                    item.removeAttribute("to");
                }
            }

            list = contentToEncode.getElementsByTagName("brute");
            for (let item of list) {
                var attr = item.getAttribute("href");
                if (attr && attr.toLowerCase().indexOf("javascript") > -1) {
                    item.removeAttribute("href");
                }
            }

            return contentToEncode;
        },

        getDesignContent: function (content) {
            return this.encodeScripts(content);
        },

        // The code below is the same because it needs to be applied when switching to HTML mode and also when content is submitted. 
        getHtmlContent: function (content) {
            return this.encodeScripts(content);
        }
    }

    MyCustomSVGFilter.registerClass('MyCustomSVGFilterFilter', Telerik.Web.UI.Editor.Filter);
</script>

As a small token of gratitude for helping us identify this, we have updated your Telerik points.

Regards,
Peter Milchev
Progress Telerik