CSP: style-src-elem

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The HTTP Content-Security-Policy (CSP) style-src-elem directive specifies valid sources for stylesheets <style> elements and <link> elements with rel="stylesheet".

CSP version 3
Directive type Fetch directive
default-src fallback

Yes. If this directive is absent, the user agent will look for the style-src directive, and if both of them are absent, fallback to default-src directive.

Syntax

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

Content-Security-Policy: style-src-elem <source>;
Content-Security-Policy: style-src-elem <source> <source>;

style-src-elem can be used in conjunction with style-src:

Content-Security-Policy: style-src <source>;
Content-Security-Policy: style-src-elem <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-eval'
Allows the use of eval() and similar methods for creating code from strings. You must include the single quotes.
'unsafe-hashes'
Allows to enable specific inline event handlers. If you only need to allow inline event handlers and not inline <script> elements or javascript: URLs, this is a safer method compared to using the unsafe-inline expression.
'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.
'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.
'report-sample'
Requires a sample of the violating code to be included in the violation report.

Examples

Specifications

Specification Status Comment
Content Security Policy Level 3
The definition of 'style-src-elem' in that specification.
Working Draft Initial definition.

Browser compatibility

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
style-src-elem
Experimental
Chrome Full support 75Edge No support NoFirefox No support No
Notes
No support No
Notes
Notes See bug 1529338.
IE No support NoOpera Full support 62Safari No support NoWebView Android Full support 75Chrome Android Full support 75Firefox Android No support No
Notes
No support No
Notes
Notes See bug 1529338.
Opera Android ? Safari iOS No support NoSamsung Internet Android No support No

Legend

Full support  
Full support
No support  
No support
Compatibility unknown  
Compatibility unknown
Experimental. Expect behavior to change in the future.
Experimental. Expect behavior to change in the future.
See implementation notes.
See implementation notes.

See also