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The HTTP Content-Security-Policy (CSP) script-src directive specifies valid sources for JavaScript. This includes not only URLs loaded directly into <script> elements, but also things like inline script event handlers (onclick) and XSLT stylesheets which can trigger script execution.

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.

Syntax

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

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

Sources

<source> can be one of the following:

<host-source>
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.
Examples:
  • http://*.example.com: Matches all attempts to load from any subdomain of example.com using the http: URL scheme.
  • mail.example.com:443: Matches all attempts to access port 443 on mail.example.com.
  • https://store.example.com: Matches all attempts to access store.example.com using https:.
<scheme-source>
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.
'self'
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.
'unsafe-inline'
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.
'unsafe-eval'
Allows the use of eval() and similar methods for creating code from strings. You must include the single quotes.
'none'
Refers to the empty set; that is, no URLs match. The single quotes are required.
'nonce-<base64-value>'
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. Specifying nonce makes a modern browser ignore 'unsafe-inline' which could still be set for older browsers without nonce support.
'<hash-algorithm>-<base64-value>'
A sha256, sha384 or sha512 hash of scripts or styles. The use of this source consists of two portions separated by a dash: the encryption algorithm used to create the hash and the base64-encoded hash of the script or style. 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. In CSP 2.0 this applied only to inline scripts. CSP 3.0 allows it in the case of script-src for external scripts.
'strict-dynamic'
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.
'report-sample'
Requires a sample of the violating code to be included in the violation report.

Examples

Violation case

Given this CSP header:

Content-Security-Policy: script-src https://example.com/

the following script is blocked and won't be loaded or executed:

<script src="https://not-example.com/js/library.js"></script>

Note that inline event handlers are blocked as well:

<button id="btn" onclick="doSomething()">

You should replaced them with addEventListener calls:

document.getElementById("btn").addEventListener('click', doSomething);

Unsafe inline script

Note: Disallowing inline styles and inline scripts is one of the biggest security wins CSP provides. However, if you absolutely have to use it, there are a few mechanisms that will allow them.

To allow inline scripts and inline event handlers, 'unsafe-inline', a nonce-source or a hash-source that matches the inline block can be specified.

Content-Security-Policy: script-src 'unsafe-inline';

The above Content Security Policy will allow inline <script> elements

<script> 
  var inline = 1; 
</script>

You can use a nonce-source to only allow specific inline script blocks:

Content-Security-Policy: script-src 'nonce-2726c7f26c'

You will have to set the same nonce on the <script> element:

<script nonce="2726c7f26c">
  var inline = 1;
</script>

Alternatively, you can create hashes from your inline scripts. CSP supports sha256, sha384 and sha512.

Content-Security-Policy: script-src 'sha256-B2yPHKaXnvFWtRChIbabYmUBFZdVfKKXHbWtWidDVF8='

When generating the hash, don't include the <script> tags and note that capitalization and whitespace matter, including leading or trailing whitespace.

<script>var inline = 1;</script>

Unsafe eval expressions

The 'unsafe-eval' source expression controls several script execution methods that create code from strings. If 'unsafe-eval' isn't specified with the script-src directive, the following methods are blocked and won't have any effect:

strict-dynamic

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. For example, a policy such as script-src 'strict-dynamic' 'nonce-R4nd0m' https://whitelisted.com/ would allow loading of a root script with <script nonce="R4nd0m" src="https://example.com/loader.js"> and propagate that trust to any script loaded by loader.js, but disallow loading scripts from https://whitelisted.com/ unless accompanied by a nonce or loaded from a trusted script.

script-src 'strict-dynamic' 'nonce-someNonce'

Or

script-src 'strict-dynamic' 'sha256-base64EncodedHash'

It is possible to deploy strict-dynamic in a backwards compatible way, without requiring user-agent sniffing.
The policy:

script-src 'unsafe-inline' https: 'nonce-abcdefg' 'strict-dynamic'

will act like'unsafe-inline' https: in browsers that support CSP1, https: 'nonce-abcdefg' in browsers that support CSP2, and 'nonce-abcdefg' 'strict-dynamic' in browsers that support CSP3.

Specifications

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

Browser compatibility

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
Basic supportChrome Full support 25Edge Full support 14Firefox Full support 23IE No support NoOpera Full support 15Safari Full support 7WebView Android Full support YesChrome Android Full support YesEdge Mobile ? Firefox Android Full support 23Opera Android ? Safari iOS Full support 7.1Samsung Internet Android Full support Yes
With external scriptsChrome Full support 59Edge ? Firefox ? IE ? Opera ? Safari ? WebView Android Full support 59Chrome Android Full support 59Edge Mobile ? Firefox Android ? Opera Android ? Safari iOS ? Samsung Internet Android Full support 7.0

Legend

Full support  
Full support
No support  
No support
Compatibility unknown  
Compatibility unknown

See also

Etiquetas do documento e colaboradores

Última atualização por: ivan-aksamentov,