The HTTP Content-Security-Policy response header allows web site administrators to control resources the user agent is allowed to load for a given page. With a few exceptions, policies mostly involve specifying server origins and script endpoints. This helps guard against cross-site scripting attacks (XSS).

For more information, see also this article on Content Security Policy (CSP).

Header type Response header
Forbidden header name no

Syntax

Content-Security-Policy: <policy-directive>; <policy-directive>

Directives

Fetch directives

Fetch directives control locations from which certain resource types may be loaded.

child-src
Defines the valid sources for web workers and nested browsing contexts loaded using elements such as <frame> and <iframe>.
connect-src
Restricts the URLs which can be loaded using script interfaces
default-src
Serves as a fallback for the other fetch directives.
font-src
Specifies valid sources for fonts loaded using @font-face.
frame-src
Specifies valid sources for nested browsing contexts loading using elements such as <frame> and <iframe>.
img-src
Specifies valid sources of images and favicons.
manifest-src
Specifies valid sources of application manifest files.
media-src
Specifies valid sources for loading media using the <audio> and <video> elements.
object-src
Specifies valid sources for the <object>, <embed>, and <applet> elements.
script-src
Specifies valid sources for JavaScript.
style-src
Specifies valid sources for stylesheets.
worker-src
Specifies valid sources for Worker, SharedWorker, or ServiceWorker scripts.

Document directives

Document directives govern the properties of a document or worker environment to which a policy applies.

base-uri
Restricts the URLs which can be used in a document's <base> element.
plugin-types
Restricts the set of plugins that can be embedded into a document by limiting the types of resources which can be loaded.
sandbox
Enables a sandbox for the requested resource similar to the <iframe> sandbox attribute.
disown-opener
Ensures a resource will disown its opener when navigated to.

Navigation directives govern to which location a user can navigate to or submit a form to, for example.

form-action
Restricts the URLs which can be used as the target of a form submissions from a given context.
frame-ancestors
Specifies valid parents that may embed a page using <frame><iframe><object><embed>, or <applet>.
navigation-to
Restricts the URLs to which a document can navigate by any means (a, form, window.location, window.open, etc.)

Reporting directives

Reporting directives control the reporting process of CSP violations. See also the Content-Security-Policy-Report-Only header.

report-uri
Instructs the user agent to report attempts to violate the Content Security Policy. These violation reports consist of JSON documents sent via an HTTP POST request to the specified URI.
report-to
Fires a SecurityPolicyViolationEvent.

Other directives

block-all-mixed-content
Prevents loading any assets using HTTP when the page is loaded using HTTPS.
referrer
Used to specify information in the referer (sic) header for links away from a page. Use the Referrer-Policy header instead.
require-sri-for
Requires the use of SRI for scripts or styles on the page.
upgrade-insecure-requests
Instructs user agents to treat all of a site's insecure URLs (those served over HTTP) as though they have been replaced with secure URLs (those served over HTTPS). This directive is intended for web sites with large numbers of insecure legacy URLs that need to be rewritten.

CSP in workers

Workers are in general not governed by the content security policy of the document (or parent worker) that created them. To specify a content security policy for the worker, set a Content-Security-Policy response header for the request which requested the worker script itself.

The exception to this is if the worker script's origin is a globally unique identifier (for example, if its URL has a scheme of data or blob). In this case, the worker does inherit the content security policy of the document or worker than created it.

Multiple content security policies

CSP allows multiple policies being specified for a resource, including via the Content-Security-Policy header, the Content-Security-Policy-Report-Only header and a <meta> element.

You can use the Content-Security-Policy header more than once like in the example below. Pay special attention to the connect-src directive here. Even though the second policy would allow the connection, the first policy contains connect-src 'none'. Adding additional policies can only further restrict the capabilities of the protected resource, which means that there will be no connection allowed and, as the strictest policy, connect-src 'none' is enforced.

Content-Security-Policy: default-src 'self' http://example.com;
                         connect-src 'none';
Content-Security-Policy: connect-src http://example.com/;
                         script-src http://example.com/

Examples

Example: Disable unsafe inline/eval, only allow loading of resources (images, fonts, scripts, etc.) over https:

// header
Content-Security-Policy: default-src https:

// meta tag
<meta http-equiv="Content-Security-Policy" content="default-src https:">

Example: Pre-existing site that uses too much inline code to fix but wants to ensure resources are loaded only over https and disable plugins:

Content-Security-Policy: default-src https: 'unsafe-eval' 'unsafe-inline'; object-src 'none'

Example: Don't implement the above policy yet; instead just report violations that would have occurred:

Content-Security-Policy-Report-Only: default-src https:; report-uri /csp-violation-report-endpoint/

See Mozilla Web Security Guidelines for more examples.

Specifications

Specification Status Comment
Content Security Policy Level 3 Editor's Draft Adds disown-opener, manifest-src, navigation-to, report-to, strict-dynamic, worker-src. Undeprecates frame-src. Deprecates report-uri in favor if report-to.
Mixed Content Candidate Recommendation Adds block-all-mixed-content.
Subresource Integrity Recommendation Adds require-sri-for.
Upgrade Insecure Requests Candidate Recommendation Adds upgrade-insecure-requests.
Content Security Policy Level 2 Recommendation Adds base-uri, child-src, form-action, frame-ancestors, plugin-types, referrer, reflected-xss, and report-uri. Deprecates frame-src.
Content Security Policy 1.0 Candidate Recommendation Defines connect-src, default-src, font-src, frame-src, img-src, media-src, object-src, report-uri, sandbox, script-src, and style-src.

Browser compatibility

Feature Chrome Edge Firefox Internet Explorer Opera Safari Servo
Basic Support2511423.021031574?
Meta element support(Yes)(Yes)45.0No support(Yes)(Yes)?
Worker support(Yes)(Yes)50.0No support?No support?
Feature Android Chrome for Android Edge Mobile Firefox for Android IE Mobile Opera Mobile Safari Mobile
Basic Support4.4(Yes)(Yes)23.0??7.15
Meta element support(Yes)(Yes)(Yes)45.0No support(Yes)(Yes)
Worker support?(Yes)(Yes)50.0No support?No support

1. Implemented as X-Webkit-CSP header in Chrome 14.

2. Implemented as X-Content-Security-Policy header in Firefox 4.

3. Implemented as X-Content-Security-Policy header, only supporting 'sandbox' directive.

4. Implemented as X-Webkit-CSP header in Safari 6.

5. Implemented as X-Webkit-CSP header in iOS 5.1.

See also

Document Tags and Contributors

 Contributors to this page: fscholz, graingert, gapple, teoli, sideshowbarker, wbamberg, jpmedley, kscarfone
 Last updated by: fscholz,