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Content Security Policy

If the strict Content-Security-Policy (CSP) mode is enabled, some browser features are disabled by default:

  • Inline JavaScript, such as <script></script> or DOM event attributes like onclick, are blocked. All script code must reside in separate files, served from a whitelisted domain.
  • Dynamic code evaluation via eval() and string arguments for both setTimeout and setInterval are blocked.

UI for ASP.NET AJAX and CSP

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

If CSP mode is enabled for a web application utilizing UI for ASP.NET AJAX, at least the unsafe-eval and unsafe-inline keywords must be added as part of the script-src section of the meta tag or HTTP header used for enabling the CSP mode.

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

Example 1: Minimal configuration to run UI for ASP.NET AJAX with CSP.

<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 to also add their domains to the script-src, style-src, font-src and img-src sections.

Example 2: Using UI for ASP.NET AJAX with CDN over HTTPS (SSL).

<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 ;
             img-src 'self' https://d35islomi5rx1v.cloudfront.net "
     />

Example 3: Using UI for ASP.NET AJAX with CDN over plain HTTP.

<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 ;
             img-src 'self' http://aspnet-skins.telerikstatic.com "
     />

If you are using a custom CDN provider, make sure to 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 (i.e., the Material skin is not used).

MS AJAX and CSP

The MS AJAX framework 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(), eval() and renders other inline scripts. Thus, it is unlikely to work without script-src 'self' 'unsafe-inline' 'unsafe-eval'.

You can easily test whether the basic MS AJAX functionality operates in your environemnt by clicking the button from Example 4 below and ensuring there are no errors, and that the request is an XmlHttpRequest and not a full postback.

Also, make sure to test the application in Release mode explicitly because the Debug mode of the MS AJAX scripts contains more eval statements than the release mode. Thus, the behavior between the local development environment and the staging/production environment may differ.

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

Example 4: Test basic MS AJAX functionality with CSP

<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>

See Also