Ember.js 1.9.1 Released

– By Tom Dale

Today, the Ember team is pleased to announce the release of Ember.js 1.9.1. Ember 1.9.1 fixes one regression and introduces more conservative escaping of attributes to help developers guard against inadvertent cross-site scripting (XSS) vulnerabilities.

{{view}} Helper & Instances

The 1.9.0 release introduced a regression where the Handlebars {{view}} helper would only work with Ember.View subclasses, not instances. In 1.9.1, passing a view instance to the helper has been fully restored.

We intended to deprecate this functionality, not remove it entirely. If your app was relying on this behavior, first, please accept our apologies for the accidental regression. Second, please consider refactoring your code to use components instead of views, as support for this API will be removed in Ember 2.0.

XSS Improvements for Bound Attributes

XSS vulnerabilities happen when you unintentionally put unescaped user-supplied content into the DOM, creating a vector for attackers to trick the browser into evaluating JavaScript that has the same access to data as your legitimate JavaScript.

Since its inception, Ember.js has automatically guarded against these attacks by HTML-escaping any bound data that goes into the DOM. For example, given this model data:

  "firstName": "<script type=javascript>alert('pwned!');</script>"

The following template would not be vulnerable to XSS:

Hello, {{firstName}}!

That's because Ember automatically replaces the < and > characters with &lt; and &gt;.

However, there is still another potential exploit vector: bound attributes.

Let's say you display a profile for your users and allow them to supply an arbitrary homepage that your app links to:

{{!-- app/templates/user.hbs --}}
First Name: {{firstName}}
Homepage: <a {{bind-attr href=homepageUrl}}>{{homepageUrl}}</a>

While this template may look harmless at first glance, imagine a malicious user provides the following data:

  "firstName": "Guardians of Peace",
  "homepageUrl": "javascript:alert('Kim Jong Un is not to be

If the attacker can induce another user to click the profile link, you will have inadvertently allowed their JavaScript to be evaluated in the same origin as your trusted code.

As of Ember 1.9.1, we will automatically escape any bound href, src or background attributes that contain a javascript: or vbscript: protocol handler by prefixing their value with unsafe:.

We are also releasing a new beta version of Ember 1.10 that contains even more targeted fixes. Thanks to the additional power the HTMLbars parser gives us, these attributes will only be escaped on elements where they trigger a top-level navigation and thus a potential exploit: a, body, link, iframe, and img.

We'd like to thank Mano and Manoharan from Zoho for responsibly disclosing this potential XSS vector and working with us to find a solution that helps developers write secure apps.