Content Security Policy Mode

If the strict Content-Security-Policy (CSP) mode is enabled, it disables the following browser features by default:

• Inline JavaScript, such as <script></script>, or DOM event attributes, such as onclick, are blocked. All script code must reside in separate files that are served from a white-listed domain.

• Dynamic code evaluation through eval() and string arguments for both setTimeout and setInterval are blocked.

Working with Telerik UI for ASP.NET AJAX

Telerik UI for ASP.NET AJAX uses eval() calls and inline <script> tags. Thus, Telerik UI for ASP.NET AJAX does not currently support the strict CSP mode.

If CSP is enabled for a web application, which utilizes Telerik UI for ASP.NET AJAX, you have to add at least the unsafe-eval and unsafe-inline keywords to the script-src section of the meta tag or HTTP header that are used for enabling the CSP mode.

To allow font icons, raster icons, and inline style attributes that are also heavily used by the Telerik UI for ASP.NET AJAX suite, you must also add the unsafe-inline keyword for the style-src section.

Minimal configuration to run Telerik UI for ASP.NET AJAX with the CSP mode

HTML

<meta
    http-equiv="Content-Security-Policy"
    content="script-src 'self' 'unsafe-inline' 'unsafe-eval'; style-src 'self' 'unsafe-inline' ;"
     />

To work with CDN, you must also add the self keyword to the font-src and img-src sections. Make sure that you also include their domains in the script-src, style-src, font-src, and img-src sections.

Using Telerik UI for ASP.NET AJAX with CDN over HTTPS (SSL)

HTML

<meta
    http-equiv="Content-Security-Policy"
    content="script-src 'self' 'unsafe-inline' 'unsafe-eval' https://d2i2wahzwrm1n5.cloudfront.net ;
			 style-src 'self' 'unsafe-inline' https://d35islomi5rx1v.cloudfront.net ;
			 font-src 'self' https://d35islomi5rx1v.cloudfront.net 'data:';
			 img-src 'self' https://d35islomi5rx1v.cloudfront.net 'data:'"
     />

Using Telerik UI for ASP.NET AJAX with CDN over plain HTTP

HTML

<meta
    http-equiv="Content-Security-Policy"
    content="script-src 'self' 'unsafe-inline' 'unsafe-eval' http://aspnet-scripts.telerikstatic.com ;
			 style-src 'self' 'unsafe-inline' http://aspnet-skins.telerikstatic.com ;
			 font-src 'self' http://aspnet-skins.telerikstatic.com 'data:';
			 img-src 'self' http://aspnet-skins.telerikstatic.com 'data:'"
     />

If you are using a custom CDN provider, replace the built-in Telerik URLs with the URLs to your host.

If you are using the Material skin, you must also add the https://fonts.gstatic.com address to the allowed URLs for fonts so that the Roboto font is allowed.

The presence of the font-src 'self' section causes Chrome to evaluate all fonts on the page and this will also trigger requests to the Google cloud for the Roboto font, even if it is not used by the page, that is, even if the Material skin is not used.

You can find more information on how to work with third-party libraries and resolved CSP-related issues in the following Telerik forum thread RadMap CSP Setting for Bing and in the Resolve Content Security Policies errors YouTube video:

Working with Microsoft AJAX

The Microsoft (MS) AJAX framework also uses eval() calls and inline <script> tags. It generates a $create() statement for each IScriptControl instance such as the Telerik UI for ASP.NET AJAX controls. They are placed in an inline <script> tag at the end of the form.

Also, the MS AJAX framework has numerous calls to setTimeout() and eval(), and renders other inline scripts. Thus, it is unlikely to work without script-src 'self' 'unsafe-inline' 'unsafe-eval'.

You can test whether the basic MS AJAX functionality operates in your environment by clicking the button from the following example, then ensuring that no errors occur and that the request is an XmlHttpRequest and not a full postback.

Also, you need to test the application in the Release mode explicitly because the Debug mode of the MS AJAX scripts contains more eval statements than the Release mode. Therefore, the behavior between the local development environment and the staging or production environment may differ.

Having an operational MS AJAX environment is essential before adding the Telerik controls to it.

Testing basic MS AJAX functionality with CSP

ASP.NET

<ol>
    <li>Make sure there are no errors and blocked resources.</li>
    <li>Click the button.</li>
    <li>Make sure it does not throw errors and that it performs a partial postback.</li>
</ol>
<asp:ScriptManager runat="server" ID="sm1" ScriptMode="Release"/>
<asp:UpdatePanel runat="server">
    <ContentTemplate>
        <asp:Button Text="I must invoke an AJAX request if things work fine" runat="server" />
    </ContentTemplate>
</asp:UpdatePanel>