CSP: form-action
The HTTP Content-Security-Policy
(CSP) form-action
directive restricts the URLs which can be used as the target of form submissions from a given context.
Warning: Whether form-action
should block redirects after a form submission is debated and browser implementations of this aspect are inconsistent (e.g. Firefox 57 doesn't block the redirects whereas Chrome 63 does).
CSP version | 2 |
---|---|
Directive type | Navigation directive |
default-src fallback |
No. Not setting this allows anything. |
Syntax
One or more sources can be set for the form-action
policy:
http
Content-Security-Policy: form-action <source>;
Content-Security-Policy: form-action <source> <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
Meta tag configuration
html
<meta http-equiv="Content-Security-Policy" content="form-action 'none'" />
Apache configuration
html
<IfModule mod_headers.c>
Header set Content-Security-Policy "form-action 'none';"
</IfModule>
Nginx configuration
add_header Content-Security-Policy "form-action 'none';"
Violation case
Using a <form>
element with an action set to inline JavaScript will result in a CSP violation.
html
<meta http-equiv="Content-Security-Policy" content="form-action 'none'" />
<form action="javascript:alert('Foo')" id="form1" method="post">
<input type="text" name="fieldName" value="fieldValue" />
<input type="submit" id="submit" value="submit" />
</form>
<!--
// Error: Refused to send form data because it violates the following
// Content Security Policy directive: "form-action 'none'".
-->
Specifications
Specification |
---|
Content Security Policy Level 3 # directive-form-action |
Browser compatibility
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