CSP: style-src-elem

CSP: style-src-elem

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

The directive does not set valid sources for inline style attributes; these are set using style-src-attr (and valid sources for all styles may be set with style-src).

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, fall back 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 any one of the values listed in CSP Source Values.

Note that this same set of values can be used in all fetch directives (and a number of other directives).

Examples

Violation cases

Given this CSP header:

Content-Security-Policy: style-src-elem https://example.com/

…the following stylesheets are blocked and won't load:

<link href="https://not-example.com/styles/main.css" rel="stylesheet" />

<style>
  #inline-style {
    background: red;
  }
</style>

<style>
  @import url("https://not-example.com/styles/print.css") print;
</style>

…as well as styles loaded using the Link header:

Link: <https://not-example.com/styles/stylesheet.css>;rel=stylesheet

Specifications

Specification
Content Security Policy Level 3
# directive-style-src-elem

Browser compatibility

Desktop Mobile
Chrome Edge Firefox Internet Explorer Opera Safari WebView Android Chrome Android Firefox for Android Opera Android Safari on IOS Samsung Internet
style-src-elem
75
79
105
preview
No
62
No
75
75
No
54
No
11.0

See also

© 2005–2022 MDN contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy/style-src-elem