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CSP: connect-src

The HTTP Content-Security-Policy (CSP) connect-src directive restricts the URLs which can be loaded using script interfaces. The APIs that are restricted are:

CSP version 1
Directive type Fetch directive
default-src fallback Yes. If this directive is absent, the user agent will look for the default-src directive.


One or more sources can be allowed for the connect-src policy:

Content-Security-Policy: connect-src <source>;
Content-Security-Policy: connect-src <source> <source>;


<source> can be one of the following:

Internet hosts by name or IP address, as well as an optional URL scheme and/or port number. The site's address may include an optional leading wildcard (the asterisk character, '*'), and you may use a wildcard (again, '*') as the port number, indicating that all legal ports are valid for the source.
  • http://* Matches all attempts to load from any subdomain of using the http: URL scheme.
  • Matches all attempts to access port 443 on
  • Matches all attempts to access using https:.
A schema such as 'http:' or 'https:'. The colon is required, single quotes shouldn't be used. You can also specify data schemas (not recommended).
  • data: Allows data: URIs to be used as a content source. This is insecure; an attacker can also inject arbitrary data: URIs. Use this sparingly and definitely not for scripts.
  • mediastream: Allows mediastream: URIs to be used as a content source.
  • blob: Allows blob: URIs to be used as a content source.
  • filesystem: Allows filesystem: URIs to be used as a content source.
Refers to the origin from which the protected document is being served, including the same URL scheme and port number. You must include the single quotes. Some browsers specifically exclude blob and filesystem from source directives. Sites needing to allow these content types can specify them using the Data attribute.
Allows the use of inline resources, such as inline <script> elements, javascript: URLs, inline event handlers, and inline <style> elements. You must include the single quotes.
Allows the use of eval() and similar methods for creating code from strings. You must include the single quotes.
Refers to the empty set; that is, no URLs match. The single quotes are required.
A whitelist for specific inline scripts using a cryptographic nonce (number used once). The server must generate a unique nonce value each time it transmits a policy. It is critical to provide an unguessable nonce, as bypassing a resource’s policy is otherwise trivial. See unsafe inline script for an example.
A sha256, sha384 or sha512 of inline scripts or styles. When generating the hash, don't include the <script> or <style> tags and note that capitalization and whitespace matter, including leading or trailing whitespace. See unsafe inline script for an example.
The strict-dynamic source expression specifies that the trust explicitly given to a script present in the markup, by accompanying it with a nonce or a hash, shall be propagated to all the scripts loaded by that root script. At the same time, any whitelist or source expressions such as 'self' or 'unsafe-inline' will be ignored. See script-src for an example.


Violation cases

Given this CSP header:

Content-Security-Policy: connect-src

The following connections are blocked and won't load:

<a ping="">

  var xhr = new XMLHttpRequest();'GET', ''); 

  var ws = new WebSocket("");

  var es = new EventSource(""); 

  navigator.sendBeacon("", { ... });


Specification Status Comment
Content Security Policy Level 3
The definition of 'connect-src' in that specification.
Editor's Draft No changes.
Content Security Policy Level 2
The definition of 'connect-src' in that specification.
Recommendation Initial definition.

Browser compatibility

FeatureChromeFirefoxEdgeInternet ExplorerOperaSafari
Basic Support2523.0114(No)157
FeatureAndroidChrome for AndroidEdge mobileFirefox for AndroidIE mobileOpera AndroidiOS Safari
Basic Support4.4(Yes)?23.0(No)?7.1

1. Prior to Firefox 50, ping attributes of <a> elements weren't covered by connect-src.

Compatibility notes

  • Prior to Firefox 23, xhr-src was used in place of the connect-src directive and only restricted the use of XMLHttpRequest.

See also

Document Tags and Contributors

 Contributors to this page: fscholz, teoli
 Last updated by: fscholz,