Content Security Policy
Content Security Policy (CSP) is a supplementary security approach which helps you prevent specific security attacks such as Cross-Site Scripting (XSS) and data-injections.
The following code shows how to turn on the strict CSP mode:
<meta http-equiv="Content-Security-Policy" content="default-src 'self'; img-src 'self'; script-src 'self' https://kendo.cdn.telerik.com https://code.jquery.com/; style-src 'self' https://kendo.cdn.telerik.com;" />
If the strict CSP mode is enabled, some browser features are disabled by default:
Inline JavaScript and CSS, such as
<script></script>
,<style></style>
, or DOM event attributes, such asonclick
, are blocked. All JavaScript and CSS code must live in separate files that are served from the allow-listed domain.Dynamic code evaluation through
eval()
and string arguments for bothsetTimeout
andsetInterval
are blocked.
(For R1 2023 SP1 and Later) Working with Telerik UI for ASP.NET Core Components
As of R1 2023 release, the Kendo UI scripts address the unsafe-eval
directive for all components except for the Spreadsheet.
For the bigger part of its core engine, the Kendo UI for jQuery Spreadsheet uses the
Function
evaluation, and rewriting the logic of the component will lead to a great number of breaking changes.
The rest of the Kendo UI components and internal mechanisms have been rewritten to discard the usage of the eval()
and new Function()
calls.
When Kendo UI components are initialized from HTML helpers or Tag Helpers, inline scripts are generated automatically after each component HTML markup. When the CSP is enabled, you will get the following error:
Refused to execute inline script because it violates the following Content Security Policy directive: "script-src 'unsafe-eval' 'self' https://kendo.cdn.telerik.com.
To resolve the issue and prevent the components from being dependent on the unsafe-eval
directive, use the following approaches:
Deferring Scripts to File
The DeferredScriptFile
method simulates loading the initialization scripts as a JS
file through middleware
to ensure strict CSP compliance. You can either use the global deferred initialization functionality to configure all Telerik UI for ASP.NET Core components as deferred globally or defer each component separately by using the Deferred
method.
Using Declarative Initialization
The 2024 Q3 release introduces the declarative initialization functionality that serializes the helper declaration as an MVVM configuration and initializes the component from the DOM elements on the client. When this feature is enabled, the inline initialization script, which is blocked by the CSP, is not generated after the component's HTML markup.
At this stage, only some of the components support the declarative initialization feature. For more information, refer to the declarative initialization documentation.
Creating Content Security Policy Templates
Most of the components support templating options, which use the Kendo UI Templates syntax, for example, Grid templates, DropDownList templates, and more. To remove the unsafe-eval
keyword from the meta
tag of your Telerik UI for ASP.NET Core application, you must convert the client templates of all components into CSP-compatible templates. For more information on the CSP-compatible templates, refer to the CSP-compatible templates section.
The example below demonstrates how to use the Template component to define a CSP-compatible client detail template of a Grid.
@(Html.Kendo().Grid<ProductViewModel>()
.Name("grid")
.Columns(columns =>
{
columns.Bound(f => f.ProductID);
})
.ClientDetailTemplate(Html.Kendo().Template().AddComponent(detailGrid => detailGrid
.Grid<CategoryViewModel>()
.Name("grid_${data.ProductID}")
.Columns(columns =>
{
columns.Bound(c => c.ProductID);
columns.Bound(c => c.CategoryID);
columns.Bound(p => p.CategoryName);
})
.Scrollable()
.Pageable()
.HtmlAttributes(new { style = "height:300px;" })
.DataSource(dataSource => dataSource
.Ajax()
.PageSize(5)
.Read(read => read.Action("CategoryDetails_Read", "Grid", new { productID = "${data.ProductID}" }))
)
))
.Pageable()
.Scrollable()
.HtmlAttributes(new { style = "height:430px;" })
.DataSource(dataSource => dataSource
.Ajax()
.PageSize(20)
.Read(read => read.Action("Products_Read", "Grid"))
)
)
@Html.Kendo().DeferredScriptFile()
@addTagHelper *, Kendo.Mvc
@{
var url = @Url.Action("CategoryDetails_Read", "Grid");
}
<kendo-grid name="grid" height="430">
<columns>
<column field="ProductID"/>
</columns>
<grid-detail-template>
<kendo-grid name="grid_${data.ProductID}" height="300">
<columns>
<column field="ProductID"/>
<column field="CategoryID"/>
<column field="CategoryName"/>
</columns>
<datasource type="DataSourceTagHelperType.Ajax" page-size="5">
<schema data="Data" total="Total" errors="Errors">
<model id="CategoryID">
<fields>
<field name="CategoryID" type="number" editable="false"></field>
<field name="CategoryName" type="string"></field>
<field name="ProductID" type="number"></field>
</fields>
</model>
</schema>
<transport>
<read url="@Html.Raw(url+"?productID=${data.ProductID}")" />
</transport>
</datasource>
<pageable enabled="true" />
<scrollable enabled="true" />
</kendo-grid>
</grid-detail-template>
<datasource type="DataSourceTagHelperType.Ajax" page-size="20">
<schema data="Data" total="Total" errors="Errors">
<model id="ProductID">
<fields>
<field name="ProductID" type="number"></field>
</fields>
</model>
</schema>
<transport>
<read url="@Url.Action("Products_Read","Grid")"/>
</transport>
</datasource>
<pageable enabled="true"/>
<scrollable enabled="true" />
</kendo-grid>
@Html.Kendo().DeferredScriptFile()
public ActionResult Products_Read([DataSourceRequest] DataSourceRequest request)
{
return Json(productsData.ToDataSourceResult(request));
}
public ActionResult CategoryDetails_Read([DataSourceRequest] DataSourceRequest request, int productID)
{
return Json(categoriesData
.Where(t => t.ProductID == productID)
.ToDataSourceResult(request));
}
For a runnable example, refer to the Template component integration with Grid demo.
The engine for the Kendo UI inline and external templates will remain available. However, if you are using the previous template syntax, you must include the usafe-eval
directive into the application meta
tag.
(Prior to R1 2023 SP1) Working with Telerik UI for ASP.NET Core Components
The Telerik UI for ASP.NET Core releases before the R1 2023 SP1 one does not support the strict CSP mode. Thus, in these previous versions, if the Content Security Policy (CSP) is enabled, you can set the script-src
policy as follows:
-
Defer the individual components:
@(Html.Kendo().PanelBar() .Name("IntroPanelBar") .Items(items => { ... }) .Deferred() )
<kendo-panelbar name="IntroPanelBar" deferred="true"> <items> ... </items> </kendo-panelbar>
-
Render the initialization logic in a script using
nonce
.<script type="text/javascript" nonce="kendoInlineScript"> @Html.Kendo().DeferredScripts(false) </script>
-
Extend the
meta
CSP tag to include theunsafe-eval
keyword and thenonce
signature for enabling the CSP mode:<meta http-equiv="Content-Security-Policy" content="script-src 'unsafe-eval' 'self' 'nonce-kendoInlineScript' https://kendo.cdn.telerik.com;">
-
Add the links used in the _Layout such as for example -
kendostatic
,jquery
, andunpkg(jszip)
:<meta http-equiv="Content-Security-Policy" content="script-src 'unsafe-eval' 'self' 'nonce-kendoInlineScript' https://cdn.kendostatic.com https://code.jquery.com https://unpkg.com/;" />