CSP: style-src-attr

CSP: style-src-attr

The HTTP Content-Security-Policy (CSP) style-src-attr directive specifies valid sources for inline styles applied to individual DOM elements.

The directive does not set valid sources for <style> elements and <link> elements with rel="stylesheet". These are set using style-src-elem (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, fallback to default-src directive.

Syntax

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

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

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

Content-Security-Policy: style-src <source>;
Content-Security-Policy: style-src-attr <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: script-src-attr 'none'

…the inline style applied to the element below not be applied:

<div style="display:none">Foo</div>

The policy would also block any styles applied in JavaScript by setting the style attribute directly, or by setting cssText:

document.querySelector('div').setAttribute('style', 'display:none;');
document.querySelector('div').style.cssText = 'display:none;';

Style properties that are set directly on the element's style property will not be blocked, allowing users to safely manipulate styles via JavaScript:

document.querySelector('div').style.display = 'none';

Note that using JavaScript might independently be blocked using the script-src CSP directive.

Specifications

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

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-attr
75
79
105
preview
No
62
No
75
75
No
54
No
11.0

See also

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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-attr