SEC Consult Vulnerability Lab Security Advisory < 20180926-0 > ======================================================================= title: Stored Cross-Site Scripting product: Progress Kendo UI Editor vulnerable version: v2018.1.221 fixed version: none, see workaround CVE number: CVE-2018-14037 impact: medium homepage: https://www.progress.com/kendo-ui found: 2018-04-23 by: M. Tomaselli (Office Munich) SEC Consult Vulnerability Lab An integrated part of SEC Consult Europe | Asia | North America https://www.sec-consult.com ======================================================================= Vendor description: ------------------- "The Editor allows users to create rich text content by means of a WYSIWYG interface. This HTML5 widget outputs identical HTML across all major browsers, follows accessibility standards and provides an API for content manipulation. The generated widget value is comprised of XHTML markup." https://www.telerik.com/kendo-ui/editor Business recommendation: ------------------------ SEC Consult recommends to implement the workarounds provided by the vendor. Vulnerability overview/description: ----------------------------------- The demo application of the Kendo UI Editor which is hosted at https://demos.telerik.com/kendo-ui/editor/api implements a Sanitizer function which should protect from cross site scripting. However, the implemented Sanitizer fails to catch certain payloads which allow an attacker to execute JavaScript in the context of the editor itself. Proof of concept: ----------------- The following, incomplete list, of payloads can be used to trigger an alert box in the API demo application of the Kendo UI Editor: https://demos.telerik.com/kendo-ui/editor/api <object data="data:text/html;base64,PHNjcmlwdD5hbGVydCgic2VjdGVzdCIpPC9zY3JpcHQ+"></object> <IFRAME SRC="javascript:alert('XSS');"></IFRAME> <META HTTP-EQUIV="refresh" CONTENT="0;url=data:text/html;base64,PHNjcmlwdD5hbGVydCgnWFNTJyk8L3NjcmlwdD4K"> After a click on the button the setValue function on line 513 of the beautified "api.js" is called: var setValue = function () { editor.value($("#value").val()); }; The value function is implemented in line 64383 of the beautified "kendo.all.js" file and defined as: value: function (html) { var body = this.body, editorNS = kendo.ui.editor, options = this.options, currentHtml = editorNS.Serializer.domToXhtml(body, options.serialization); if (html === undefined) { return currentHtml; } if (html == currentHtml) { return; } editorNS.Serializer.htmlToDom(html, body, options.deserialization); this.selectionRestorePoint = null; this.update(); this.toolbar.refreshTools(); }, In order to mitigate certain XSS payloads the editorNS.Serializer.htmlToDom() function is called which can be seen in the excerpt below: var Serializer = { toEditableHtml: function (html) { return (html || '').replace(/<!\[CDATA\[(.*)?\]\]>/g, '<!--[CDATA[$1]]-->').replace(/<(\/?)script([^>]*)>/gi, '<$1k:script$2>').replace(/<img([^>]*)>/gi, function (match) { return match.replace(onerrorRe, ''); }).replace(/(<\/?img[^>]*>)[\r\n\v\f\t ]+/gi, '$1').replace(/^<(table|blockquote)/i, br + '<$1').replace(/^[\s]*(&nbsp;|\u00a0)/i, '$1').replace(/<\/(table|blockquote)>$/i, '</$1>' + br); }, Although certain payloads are detected and sanitized by the function, the implemented protection fails to detect the data uri payload. The payload is added unescaped to the editor DOM after several other functions calls. Vulnerable / tested versions: ----------------------------- The following version has been identified to be vulnerable: * v2018.1.221 Vendor contact timeline: ------------------------ 2018-05-02: Contacting vendor through email for security contact 2018-05-02: Contact person requests to obtain advisory via unencrypted mail 2018-05-08: Advisory delivered through unencrypted email to vendor 2018-05-29: Contacting vendor for current status and informing them about the publishing date 2018-07-02: Reminded the vendor that the advisory will be published soon 2018-07-02: Multiple emails exchanged, vendor demands that customers need to issue a support ticket on this case 2018-07-03: Telling them that it is a security issue they already know two months without seemingly acting upon it. Vendor: product managers have been informed and will contact us; no further info 2018-07-11: Asking vendor again for a status update & patch information 2018-07-11: Vendor: "Thank you for following up. I have sent this to the product team to take into consideration. They will be following up with you as they may need. We appreciate you following up regarding this request." 2018-07-12: Detailed answer from vendor regarding workaround 2018-07-13: Requested CVE number 2018-09-26: Public release of security advisory Solution: --------- There is no fix available from the vendor. Check the vendor's website for potential future updates. Workaround: ----------- The following workaround was provided by the vendor which has to be extended in order to mitigate all of the above mentioned payloads. ```quote First, one thing to keep in mind with the Kendo UI Editor is that since it is a HTML editor that many users implement in order take advantage of HTML content (compared to straight text). This means that while we often sanitize many things (script tags, DOM event attributes, etc.) in order to prevent cross-site scripting [...] there are certain cases that we cannot automatically sanitize because of use cases that customers of ours have a this being one of them. Because the value that is set to the Editor is done through the jQuery method `$(a#valuea).val()` it is possible to sanitize or encode values before being set to the editor. This is can be done through implementing some custom sanitations through the `serialization.custom <https://docs.telerik.com/kendo-ui/api/javascript/ui/editor/configuration/serialization.custom>`, and `deserialization.custom<https://docs.telerik.com/kendo-ui/api/javascript/ui/editor/configuration/deserialization>`, options available in the Editor today. ``` ```html <!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>Untitled</title> <link rel="stylesheet" href="https://kendo.cdn.telerik.com/2018.2.620/styles/kendo.common.min.css"> <link rel="stylesheet" href="https://kendo.cdn.telerik.com/2018.2.620/styles/kendo.rtl.min.css"> <link rel="stylesheet" href="https://kendo.cdn.telerik.com/2018.2.620/styles/kendo.default.min.css"> <link rel="stylesheet" href="https://kendo.cdn.telerik.com/2018.2.620/styles/kendo.mobile.all.min.css"> <script src="https://code.jquery.com/jquery-1.12.3.min.js"></script> <script src="https://kendo.cdn.telerik.com/2018.2.620/js/angular.min.js"></script> <script src="https://kendo.cdn.telerik.com/2018.2.620/js/jszip.min.js"></script> <script src="https://kendo.cdn.telerik.com/2018.2.620/js/kendo.all.min.js"></script></head> <body> <textarea id="editor"></textarea> <script> function sanitizeHtml(html) { var temp = $("<div></div>").html(html); temp.find("object").remove(); return temp.html() || "\ufeff"; } $("#editor").kendoEditor({ tools: [ "viewHtml" ], deserialization: { custom: function(html) { return sanitizeHtml(html); } }, serialization: { custom: function(html) { return sanitizeHtml(html); } } }); var editor = $("#editor").getKendoEditor(); editor.value('<object data="data:text/html;base64,PHNjcmlwdD5hbGVydCgic2VjdGVzdCIpPC9zY3JpcHQ+"></object>'); console.log(editor.value()); </script> </body> </html> ``` Advisory URL: ------------- https://www.sec-consult.com/en/vulnerability-lab/advisories/index.html ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ SEC Consult Vulnerability Lab SEC Consult Europe | Asia | North America About SEC Consult Vulnerability Lab The SEC Consult Vulnerability Lab is an integrated part of SEC Consult. It ensures the continued knowledge gain of SEC Consult in the field of network and application security to stay ahead of the attacker. The SEC Consult Vulnerability Lab supports high-quality penetration testing and the evaluation of new offensive and defensive technologies for our customers. Hence our customers obtain the most current information about vulnerabilities and valid recommendation about the risk profile of new technologies. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Interested to work with the experts of SEC Consult? Send us your application https://www.sec-consult.com/en/career/index.html Interested in improving your cyber security with the experts of SEC Consult? Contact our local offices https://www.sec-consult.com/en/contact/index.html ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Mail: research at sec-consult dot com Web: https://www.sec-consult.com Blog: http://blog.sec-consult.com Twitter: https://twitter.com/sec_consult EOF M. Tomaselli / @2018