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2014-07-03-CSP-2-LCWD.html
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2014-07-03-CSP-2-LCWD.html
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<!DOCTYPE html><html lang=en><head>
<meta content="text/html; charset=utf-8" http-equiv=Content-Type>
<title>Content Security Policy Level 2</title>
<link href=./default.css rel=stylesheet type=text/css>
<link href=https://www.w3.org/StyleSheets/TR/W3C-LC rel=stylesheet type=text/css>
<style>
table {
text-align: left;
margin: 20px;
width: 100%;
border-collapse: collapse;
}
tbody tr:nth-child(odd) {
background-color: #EEE;
}
th {
border-bottom: 1px solid #999;
padding: 0.5em;
}
td:first-child {
width: 30%;
padding-right: 1em;
}
td {
vertical-align: top;
padding: 0.5em;
}
tbody th {
border: 0;
background-color: #FFF;
}
tr.section {
border-top: 1px solid #999;
vertical-align: top;
}
</style>
</head>
<body class=h-entry>
<div class=head>
<p data-fill-with=logo><a class=logo href=http://www.w3.org/>
<img alt=W3C height=48 src=https://www.w3.org/Icons/w3c_home width=72>
</a>
</p>
<h1 class="p-name no-ref" id=title>Content Security Policy Level 2</h1>
<h2 class="no-num no-toc no-ref heading settled heading" id=subtitle><span class=content>W3C Last Call Working Draft,
<span class=dt-updated><span class=value-title title=20140703>03 July 2014</span></span></span></h2>
<div data-fill-with=spec-metadata><dl><dt>Feedback:<dd><a href="mailto:public-webappsec@w3.org?subject=%5BCSP%5D%20feedback">public-webappsec@w3.org</a>
with subject line
“<kbd>[CSP] <var>… message topic …</var></kbd>”(<a U00027="" href=http://lists.w3.org/Archives/Public/public-webappsec/ rel=discussion>archives</a>)<dt>Editor’s Draft:<dd><a href=https://w3c.github.io/webappsec/specs/content-security-policy/>https://w3c.github.io/webappsec/specs/content-security-policy/</a><dt>Former Editors:<dd><dd class="p-author h-card vcard"><a class="p-name fn u-email email" href=mailto:brandon@hackmill.com>Brandon Sterne</a> (<span class="p-org org">formerly of Mozilla Corporation</span>)<dt>Editors:<dd><dd class="p-author h-card vcard"><a class="p-name fn u-email email" href=mailto:mkwst@google.com>Mike West</a> (<span class="p-org org">Google Inc.</span>)<dd><dd class="p-author h-card vcard"><a class="p-name fn u-email email" href=mailto:w3c@adambarth.com>Adam Barth</a> (<span class="p-org org">Google Inc.</span>)<dd><dd class="p-author h-card vcard"><a class="p-name fn u-email email" href=mailto:dveditz@mozilla.com>Dan Veditz</a> (<span class="p-org org">Mozilla Corporation</span>)<dt>Latest version:<dd><a href=http://www.w3c.org/TR/CSP/>http://www.w3c.org/TR/CSP/</a><dt>This version:<dd><a class=u-url href=http://www.w3.org/TR/2014/WD-CSP-2-20140703/>http://www.w3.org/TR/2014/WD-CSP-2-20140703/</a></dl></div>
<div data-fill-with=warning></div>
<p class=copyright data-fill-with=copyright><a href=http://www.w3.org/Consortium/Legal/ipr-notice#Copyright>Copyright</a> © 2014
<a href=http://www.w3.org/><abbr title="World Wide Web Consortium">W3C</abbr></a><sup>®</sup>
(<a href=http://www.csail.mit.edu/><abbr title="Massachusetts Institute of Technology">MIT</abbr></a>,
<a href=http://www.ercim.eu/><abbr title="European Research Consortium for Informatics and Mathematics">ERCIM</abbr></a>,
<a href=http://www.keio.ac.jp/>Keio</a>, <a href=http://ev.buaa.edu.cn/>Beihang</a>),
All Rights Reserved.
<abbr title="World Wide Web Consortium">W3C</abbr> <a href=http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer>liability</a>,
<a href=http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks>trademark</a> and
<a href=http://www.w3.org/Consortium/Legal/copyright-documents>document use</a>
rules apply.
</p>
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc no-ref heading settled heading" id=abstract><span class=content>Abstract</span></h2>
<p class=p-summary data-fill-with=abstract><p>This document defines a policy language used to declare a set of content restrictions for a web resource, and a mechanism for transmitting the policy from a server to a client where the policy is enforced.</p>
</p>
<h2 class="no-num no-toc no-ref heading settled heading" id=status><span class=content>Status of this document</span></h2>
<div data-fill-with=status><p>
<em>This section describes the status of this document at the time of
its publication. Other documents may supersede this document. A list of
current W3C publications and the latest revision of this technical report
can be found in the <a href=http://www.w3.org/TR/>W3C technical reports
index at http://www.w3.org/TR/.</a></em>
<p>
This document was published by the
<a href=http://www.w3.org/2011/webappsec/>Web Application Security Working Group</a>
as a Working Draft. This document is intended to become a W3C Recommendation.
<p>
The (<a href=http://lists.w3.org/Archives/Public/public-webappsec/>archived</a>) public mailing list
<a href="mailto:public-webappsec@w3.org?Subject=%5BCSP%5D%20PUT%20SUBJECT%20HERE">public-webappsec@w3.org</a>
(see <a href=http://www.w3.org/Mail/Request>instructions</a>)
is preferred for discussion of this specification.
When sending e-mail,
please put the text “CSP” in the subject,
preferably like this:
“[CSP] <em>…summary of comment…</em>”
<p>
Publication as a Last Call Working Draft does not imply endorsement by the W3C
Membership. This is a draft document and may be updated, replaced or
obsoleted by other documents at any time. It is inappropriate to cite this
document as other than work in progress.
<p>
This document was produced by the
<a href=http://www.w3.org/2011/webappsec/>Web Application Security Working Group</a>.
<p>
This document was produced by a group operating under
the <a href=http://www.w3.org/Consortium/Patent-Policy-20040205/>5 February 2004 W3C Patent Policy</a>.
W3C maintains a <a href=http://www.w3.org/2004/01/pp-impl/32061/status rel=disclosure>public list of any patent disclosures</a>
made in connection with the deliverables of the group;
that page also includes instructions for disclosing a patent.
An individual who has actual knowledge of a patent which the individual believes contains <a href=http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential>Essential Claim(s)</a>
must disclose the information in accordance with <a href=http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure>section 6 of the W3C Patent Policy</a>.
<p>
This specification is a <strong>Last Call Working Draft</strong>. All
persons are encouraged to review this document and <strong>send comments
to the <a href=http://lists.w3.org/Archives/Public/public-webappsec/>public-webappsec</a>
mailing list</strong> as described above. The <strong>deadline for
comments</strong> is <strong>13 August 2014</strong>.
</div>
<div data-fill-with=at-risk><p>The following features are at-risk, and may be dropped during the CR period:
<ul><li>The <a data-link-type=dfn href=#referrer title=referrer>referrer</a> directive.<li>The <a data-link-type=dfn href=#reflected-xss title=reflected-xss>reflected-xss</a> directive.</ul></div>
<h2 class="no-num no-toc no-ref heading settled heading" id=contents><span class=content>Table of Contents</span></h2>
<div data-fill-with=table-of-contents><ul class=toc>
<li><a href=#intro><span class=secno>1</span>Introduction</a>
<li><a href=#key-concepts><span class=secno>2</span>Key Concepts and Terminology</a>
<li><a href=#policy-delivery><span class=secno>3</span>Policy Delivery</a>
<ul class=toc>
<li><a href=#content-security-policy-header-field><span class=secno>3.1</span> <code>Content-Security-Policy</code> Header Field </a>
<li><a href=#content-security-policy-report-only-header-field><span class=secno>3.2</span> <code>Content-Security-Policy-Report-Only</code> Header Field </a>
<li><a href=#delivery-html-meta-element><span class=secno>3.3</span> HTML <code><span data-link-type=element title=meta>meta</span></code> Element </a>
<li><a href=#ch-csp-client-hint><span class=secno>3.4</span>The <code>CH-CSP</code> Client Hint</a>
<li><a href=#enforcing-multiple-policies><span class=secno>3.5</span>Enforcing multiple policies.</a>
<li><a href=#which-policy-applies><span class=secno>3.6</span>Policy applicability</a></ul>
<li><a href=#syntax-and-algorithms><span class=secno>4</span>Syntax and Algorithms</a>
<ul class=toc>
<li><a href=#policy-syntax><span class=secno>4.1</span>Policy Syntax</a>
<ul class=toc>
<li><a href=#policy-parsing><span class=secno>4.1.1</span>Parsing Policies</a></ul>
<li><a href=#source-list-syntax><span class=secno>4.2</span>Source List Syntax</a>
<ul class=toc>
<li><a href=#source-list-parsing><span class=secno>4.2.1</span>Parsing Source Lists</a>
<li><a href=#match-source-expression><span class=secno>4.2.2</span>Matching Source Expressions</a>
<ul class=toc>
<li><a href=#source-list-guid-matching><span class=secno>4.2.2.1</span> Security Considerations for GUID URI schemes </a>
<li><a href=#source-list-path-patching><span class=secno>4.2.2.2</span>Path Matching</a>
<li><a href=#source-list-paths-and-redirects><span class=secno>4.2.2.3</span>Paths and Redirects</a></ul>
<li><a href=#script-src-the-nonce-attribute><span class=secno>4.2.3</span> The <code>nonce</code> attribute </a>
<li><a href=#source-list-valid-nonces><span class=secno>4.2.4</span>Valid Nonces</a>
<li><a href=#source-list-valid-hashes><span class=secno>4.2.5</span>Valid Hashes</a></ul>
<li><a href=#media-type-list><span class=secno>4.3</span>Media Type List</a>
<ul class=toc>
<li><a href=#media-type-list-parsing><span class=secno>4.3.1</span>Parsing</a>
<li><a href=#media-type-list-matching><span class=secno>4.3.2</span>Matching</a></ul>
<li><a href=#violation-reports><span class=secno>4.4</span>Reporting</a></ul>
<li><a href=#processing-model><span class=secno>5</span>Processing Model</a>
<ul class=toc>
<li><a href=#processing-model-workers><span class=secno>5.1</span>Workers</a>
<li><a href=#processing-model-iframe-srcdoc><span class=secno>5.2</span><code>srcdoc</code> IFrames</a></ul>
<li><a href=#script-interfaces><span class=secno>6</span>Script Interfaces</a>
<ul class=toc>
<li><a href=#securitypolicyviolationevent-interface><span class=secno>6.1</span> <code>SecurityPolicyViolationEvent</code> Interface </a>
<li><a href=#securitypolicyviolationeventinit-interface><span class=secno>6.2</span> <code>SecurityPolicyViolationEventInit</code> Interface </a>
<li><a href=#firing-securitypolicyviolationevent-events><span class=secno>6.3</span>Firing Violation Events</a></ul>
<li><a href=#sec-directives><span class=secno>7</span>Directives</a>
<ul class=toc>
<li><a href=#directive-base-uri><span class=secno>7.1</span><code>base-uri</code></a>
<li><a href=#directive-child-src><span class=secno>7.2</span><code>child-src</code></a>
<ul class=toc>
<li><a href=#directive-child-src-nested><span class=secno>7.2.1</span>Nested Browsing Contexts</a>
<li><a href=#directive-child-src-workers><span class=secno>7.2.2</span>Workers</a></ul>
<li><a href=#directive-connect-src><span class=secno>7.3</span><code>connect-src</code></a>
<ul class=toc>
<li><a href=#connect-src-usage><span class=secno>7.3.1</span>Usage</a></ul>
<li><a href=#directive-default-src><span class=secno>7.4</span><code>default-src</code></a>
<ul class=toc>
<li><a href=#default-src-usage><span class=secno>7.4.1</span>Usage</a></ul>
<li><a href=#directive-font-src><span class=secno>7.5</span><code>font-src</code></a>
<li><a href=#directive-form-action><span class=secno>7.6</span><code>form-action</code></a>
<li><a href=#directive-frame-ancestors><span class=secno>7.7</span><code>frame-ancestors</code></a>
<ul class=toc>
<li><a href=#frame-ancestors-and-frame-options><span class=secno>7.7.1</span> Relation to <code>X-Frame-Options</code> </a>
<li><a href=#frame-ancestors-multiple-source-values><span class=secno>7.7.2</span>Multiple Host Source Values</a></ul>
<li><a href=#directive-frame-src><span class=secno>7.8</span><code>frame-src</code></a>
<li><a href=#directive-img-src><span class=secno>7.9</span><code>img-src</code></a>
<li><a href=#directive-media-src><span class=secno>7.10</span><code>media-src</code></a>
<li><a href=#directive-object-src><span class=secno>7.11</span><code>object-src</code></a>
<li><a href=#directive-plugin-types><span class=secno>7.12</span><code>plugin-types</code></a>
<ul class=toc>
<li><a href=#plugin-types-usage><span class=secno>7.12.1</span>Usage</a>
<li><a href=#plugin-types-predeclaration><span class=secno>7.12.2</span> Predeclaration of expected media types </a></ul>
<li><a href=#directive-referrer><span class=secno>7.13</span><code>referrer</code></a>
<ul class=toc>
<li><a href=#referrer-multiple-policies><span class=secno>7.13.1</span>Processing multiple referrer policies</a>
<ul class=toc>
<li><a href=#referrer-usage><span class=secno>7.13.1.1</span>Usage</a></ul></ul>
<li><a href=#directive-reflected-xss><span class=secno>7.14</span><code>reflected-xss</code></a>
<ul class=toc>
<li><a href=#reflected-xss-and-x-xss-protection><span class=secno>7.14.1</span> Relationship to <code>X-XSS-Protection</code> </a></ul>
<li><a href=#directive-report-uri><span class=secno>7.15</span><code>report-uri</code></a>
<li><a href=#directive-sandbox><span class=secno>7.16</span><code>sandbox</code></a>
<ul class=toc>
<li><a href=#sandbox-usage><span class=secno>7.16.1</span>Usage</a></ul>
<li><a href=#directive-script-src><span class=secno>7.17</span><code>script-src</code></a>
<ul class=toc>
<li><a href=#script-src-nonce-usage><span class=secno>7.17.1</span> Nonce usage for <code><span data-link-type=element title=script>script</span></code> elements </a>
<li><a href=#script-src-hash-usage><span class=secno>7.17.2</span> Hash usage for <code><span data-link-type=element title=script>script</span></code> elements </a></ul>
<li><a href=#directive-style-src><span class=secno>7.18</span><code>style-src</code></a>
<ul class=toc>
<li><a href=#style-src-nonce-usage><span class=secno>7.18.1</span> Nonce usage for <code><span data-link-type=element title=style>style</span></code> elements </a>
<li><a href=#style-src-hash-usage><span class=secno>7.18.2</span> Hash usage for <code><span data-link-type=element title=style>style</span></code> elements </a></ul></ul>
<li><a href=#examples><span class=secno>8</span>Examples</a>
<ul class=toc>
<li><a href=#example-policies><span class=secno>8.1</span>Sample Policy Definitions</a>
<li><a href=#example-violation-report><span class=secno>8.2</span>Sample Violation Report</a></ul>
<li><a href=#security-considerations><span class=secno>9</span>Security Considerations</a>
<ul class=toc>
<li><a href=#security-css-parsing><span class=secno>9.1</span>Cascading Style Sheet (CSS) Parsing</a>
<li><a href=#security-violation-reports><span class=secno>9.2</span>Violation Reports</a></ul>
<li><a href=#implementation-considerations><span class=secno>10</span>Implementation Considerations</a>
<li><a href=#iana-considerations><span class=secno>11</span>IANA Considerations</a>
<ul class=toc>
<li><a href=#iana-content-security-policy><span class=secno>11.1</span>Content-Security-Policy</a>
<li><a href=#iana-content-security-policy-report-only><span class=secno>11.2</span>Content-Security-Policy-Report-Only</a>
<li><a href=#iana-ch-csp><span class=secno>11.3</span>CH-CSP</a></ul>
<li><a href=#acknowledgements><span class=secno>12</span>Acknowledgements</a>
<li><a href=#conformance><span class=secno></span>Conformance</a>
<ul class=toc>
<li><a href=#conventions><span class=secno></span>Document conventions</a>
<li><a href=#conformant-algorithms><span class=secno></span>Conformant Algorithms</a>
<li><a href=#conformance-classes><span class=secno></span>Conformance Classes</a></ul>
<li><a href=#references><span class=secno></span> References</a>
<ul class=toc>
<li><a href=#normative><span class=secno></span> Normative References</a>
<li><a href=#informative><span class=secno></span> Informative References</a></ul>
<li><a href=#index><span class=secno></span> Index</a></ul></div>
<section>
<h2 class="heading settled heading" data-level=1 id=intro><span class=secno>1 </span><span class=content>Introduction</span><a class=self-link href=#intro></a></h2>
<p><em>This section is not normative.</em></p>
<p>This document defines Content Security Policy, a mechanism web applications
can use to mitigate a broad class of content injection vulnerabilities, such
as cross-site scripting (XSS). Content Security Policy is a declarative policy
that lets the authors (or server administrators) of a web application inform
the client about the sources from which the application expects to load
resources.</p>
<p>To mitigate XSS attacks, for example, a web application can declare that it
only expects to load script from specific, trusted sources. This declaration
allows the client to detect and block malicious scripts injected into the
application by an attacker.</p>
<p>Content Security Policy (CSP) is not intended as a first line of defense
against content injection vulnerabilities. Instead, CSP is best used as
defense-in-depth, to reduce the harm caused by content injection attacks. As
a first line of defense against content injection, server operators should
validate their input and encode their output.</p>
<p>There is often a non-trivial amount of work required to apply CSP to an
existing web application. To reap the greatest benefit, authors will need to
move all inline script and style out-of-line, for example into external
scripts, because the user agent cannot determine whether an inline script
was injected by an attacker.</p>
<p>To take advantage of CSP, a web application opts into using CSP by supplying a
<code>Content-Security-Policy</code> HTTP header. Such policies apply to the
current resource representation only. To supply a policy for an entire site,
the server needs to supply a policy with each resource representation.</p>
</section>
<section>
<h2 class="heading settled heading" data-level=2 id=key-concepts><span class=secno>2 </span><span class=content>Key Concepts and Terminology</span><a class=self-link href=#key-concepts></a></h2>
<p>This section defines several terms used throughout the document.</p>
<p>The term <dfn data-dfn-type=dfn data-export="" id=security-policy title="security policy|policy">security policy<a class=self-link href=#security-policy></a></dfn>
refers to either:</p>
<ol>
<li>a set of security preferences for restrictions within which
the content can operate, or</li>
<li>a fragment of text that codifies these preferences.</li>
</ol>
<p>The security policies defined by this document are applied by a
user agent on a <em>per-resource representation basis</em>.
Specifically, when a user agent receives a policy along with the
representation of a given resource, that policy applies to <em>that
resource representation only</em>. This document often refers to
that resource representation as the <dfn data-dfn-type=dfn data-export="" id=protected-resource>protected resource<a class=self-link href=#protected-resource></a></dfn>.</p>
<p>A <dfn data-dfn-type=dfn data-export="" id=security-policy-directive title="security policy directive|directive">security policy
directive<a class=self-link href=#security-policy-directive></a></dfn> is a portion of a <a data-link-type=dfn href=#security-policy title=policy>policy</a> that declares the specific
set of restrictions for a particular resource type, or which manipulates a
specific aspect of a protected resource’s configuration. A server transmits
its security policy for a particular protected resource as a collection of
directives, such as <code><a data-link-type=dfn href=#default-src title=default-src>default-src</a> 'self'</code>, each of which
declares a specific set of restrictions for that resource as instantiated
by the user agent. More details are provided in the
<a data-section="" href=#sec-directives>§7 Directives</a> section.</p>
<p>A directive consists of a <dfn data-dfn-type=dfn data-noexport="" id=directive-name0>directive name<a class=self-link href=#directive-name0></a></dfn>, which
indicates the privileges controlled by the directive, and a
<dfn data-dfn-type=dfn data-noexport="" id=directive-value0>directive value<a class=self-link href=#directive-value0></a></dfn>, which specifies the restrictions the
policy imposes on those privileges.</p>
The term <dfn data-dfn-type=dfn data-noexport="" id=origin>origin<a class=self-link href=#origin></a></dfn> is defined in the Origin specification.
<a data-biblio-type=normative data-link-type=biblio href=#biblio-rfc6454 title=biblio-rfc6454>[RFC6454]</a>
<p>The term <dfn data-dfn-type=dfn data-noexport="" id=globally-unique-identifier>globally unique identifier<a class=self-link href=#globally-unique-identifier></a></dfn> is defined in section 4 of
the Origin specification. Note that URLs that do not use hierarchical
elements as naming authorities have origins which are globally unique
identifiers. <a data-biblio-type=normative data-link-type=biblio href=#biblio-rfc6454 title=biblio-rfc6454>[RFC6454]</a></p>
<p>The term <dfn data-dfn-type=dfn data-noexport="" id=uri>URI<a class=self-link href=#uri></a></dfn> is defined in the URI specification. <a data-biblio-type=normative data-link-type=biblio href=#biblio-uri title=biblio-uri>[URI]</a></p>
<p>The term <dfn data-dfn-type=dfn data-noexport="" id=resource-representation>resource representation<a class=self-link href=#resource-representation></a></dfn> is defined
<a href=http://tools.ietf.org/html/rfc7231#section-3>Section 3</a>
of HTTP/1.1 -- Semantics and Content <a data-biblio-type=normative data-link-type=biblio href=#biblio-rfc7231 title=biblio-rfc7231>[RFC7231]</a></p>
<p>The terms <dfn data-dfn-type=dfn data-noexport="" id=json-object>JSON object<a class=self-link href=#json-object></a></dfn> and <dfn data-dfn-type=dfn data-noexport="" id=json-stringification>JSON stringification<a class=self-link href=#json-stringification></a></dfn> are
defined in the JSON specification. <a data-biblio-type=normative data-link-type=biblio href=#biblio-rfc4627 title=biblio-rfc4627>[RFC4627]</a></p>
<p>The <code><a data-link-type=element href=http://www.w3.org/TR/html5/obsolete.html#the-applet-element title=applet>applet</a></code>, <code><a data-link-type=element href=http://www.w3.org/TR/html5/embedded-content-0.html#audio title=audio>audio</a></code>,
<code><a data-link-type=element href=http://www.w3.org/TR/html5/embedded-content-0.html#the-embed-element title=embed>embed</a></code>, <code><a data-link-type=element href=http://www.w3.org/TR/html5/embedded-content-0.html#the-iframe-element title=iframe>iframe</a></code>,
<code><a data-link-type=element href=http://www.w3.org/TR/html5/embedded-content-0.html#the-img-element title=img>img</a></code>, <code><a data-link-type=element href=http://www.w3.org/TR/html5/document-metadata.html#the-link-element title=link>link</a></code>,
<code><a data-link-type=element href=http://www.w3.org/TR/html5/embedded-content-0.html#the-object-element title=object>object</a></code>, <code><a data-link-type=element href=http://www.w3.org/TR/html5/scripting-1.html#script title=script>script</a></code>,
<code><a data-link-type=element href=http://www.w3.org/TR/html5/embedded-content-0.html#the-source-element title=source>source</a></code>, <code><a data-link-type=element href=http://www.w3.org/TR/html5/embedded-content-0.html#the-track-element title=track>track</a></code>, and
<code><a data-link-type=element href=http://www.w3.org/TR/html5/embedded-content-0.html#video title=video>video</a></code> elements are defined in the HTML5
specification. <a data-biblio-type=normative data-link-type=biblio href=#biblio-html5 title=biblio-html5>[HTML5]</a></p>
<p>The terms <a data-link-type=dfn href=http://www.w3.org/TR/html5/browsers.html#auxiliary-browsing-context title="auxiliary browsing contexts">auxiliary browsing contexts</a>,
<a data-link-type=dfn href=http://www.w3.org/TR/html5/browsers.html#opener-browsing-context title="opener browsing context">opener browsing context</a>, and <a data-link-type=dfn href=http://www.w3.org/TR/html5/browsers.html#nested-browsing-context title="nested browsing contexts">nested browsing contexts</a> are
defined in the HTML5 specification. <a data-biblio-type=normative data-link-type=biblio href=#biblio-html5 title=biblio-html5>[HTML5]</a></p>
<p>A <a data-link-type=dfn href=http://www.w3.org/TR/html5/infrastructure.html#plugin title=plugin>plugin</a> is defined in the HTML5 specification. <a data-biblio-type=normative data-link-type=biblio href=#biblio-html5 title=biblio-html5>[HTML5]</a></p>
<p>The <code><a class="production css-code" data-link-type=at-rule href=http://www.w3.org/TR/css-fonts-3/#at-font-face-rule title=@font-face><@font-face></a></code> Cascading Style Sheets (CSS) rule is defined
in the CSS Fonts Module Level 3 specification. <a data-biblio-type=normative data-link-type=biblio href=#biblio-css3-fonts title=biblio-css3-fonts>[CSS3-FONTS]</a></p>
<p>The <code>XMLHttpRequest</code> object is defined in the
<code>XMLHttpRequest</code> specification. <a data-biblio-type=normative data-link-type=biblio href=#biblio-xmlhttprequest title=biblio-xmlhttprequest>[XMLHTTPREQUEST]</a></p>
<p>The <code>WebSocket</code> object is defined in the <code>WebSocket</code>
specification. <a data-biblio-type=normative data-link-type=biblio href=#biblio-websockets title=biblio-websockets>[WEBSOCKETS]</a></p>
<p>The <code>EventSource</code> object is defined in the <code>EventSource</code>
specification. <a data-biblio-type=normative data-link-type=biblio href=#biblio-eventsource title=biblio-eventsource>[EVENTSOURCE]</a></p>
<p>The Augmented Backus-Naur Form (ABNF) notation used in this document is
specified in RFC5234. <a data-biblio-type=normative data-link-type=biblio href=#biblio-abnf title=biblio-abnf>[ABNF]</a></p>
<p>This document also uses the ABNF extension "#rule" as defined in
<a href=http://tools.ietf.org/html/rfc7230#section-7>Section 7</a>
of HTTP/1.1 -- Message Syntax and Routing. <a data-biblio-type=normative data-link-type=biblio href=#biblio-rfc7230 title=biblio-rfc7230>[RFC7230]</a></p>
<p>The following core rules are included by reference, as defined in
<a href=http://tools.ietf.org/html/rfc5234#appendix-B.1>Appendix B.1</a>
of <a data-biblio-type=normative data-link-type=biblio href=#biblio-abnf title=biblio-abnf>[ABNF]</a>: <code>ALPHA</code> (letters), <code>DIGIT</code> (decimal
0-9), <code>WSP</code> (white space) and <code>VCHAR</code> (printing
characters).</p>
<p><dfn data-dfn-type=dfn data-noexport="" id=sha-256>SHA-256<a class=self-link href=#sha-256></a></dfn>, <dfn data-dfn-type=dfn data-noexport="" id=sha-384>SHA-384<a class=self-link href=#sha-384></a></dfn>, and <dfn data-dfn-type=dfn data-noexport="" id=sha-512>SHA-512<a class=self-link href=#sha-512></a></dfn> are the digest
algorithms <a href=http://csrc.nist.gov/groups/STM/cavp/documents/shs/sha256-384-512.pdf>defined by the NIST</a>.</p>
<p>The <dfn data-dfn-type=dfn data-noexport="" id=runs-a-worker>runs a worker<a class=self-link href=#runs-a-worker></a></dfn> algorithm is
<a href=http://www.w3.org/TR/workers/#run-a-worker>defined in the Web
Workers spec</a>. <a data-biblio-type=normative data-link-type=biblio href=#biblio-workers title=biblio-workers>[WORKERS]</a></p>
<p>The term <dfn data-dfn-type=dfn data-noexport="" id=callable>callable<a class=self-link href=#callable></a></dfn> refers to an object whose interface
has one or more <dfn data-dfn-type=dfn data-noexport="" id=callers>callers<a class=self-link href=#callers></a></dfn> as defined in the <a href=http://www.w3.org/TR/2010/WD-WebIDL-20101021/#idl-callers>Web
IDL</a> specification <a data-biblio-type=normative data-link-type=biblio href=#biblio-webidl title=biblio-webidl>[WEBIDL]</a>.</p>
<p>An <dfn data-dfn-type=dfn data-noexport="" id=http-200-response>HTTP 200 response<a class=self-link href=#http-200-response></a></dfn> is defined in
<a href=http://tools.ietf.org/html/rfc7231#section-6.3.1>Section 6.3.1</a>
of HTTP/1.1 -- Semantics and Content <a data-biblio-type=normative data-link-type=biblio href=#biblio-rfc7231 title=biblio-rfc7231>[RFC7231]</a></p>
</section>
<section>
<h2 class="heading settled heading" data-level=3 id=policy-delivery><span class=secno>3 </span><span class=content>Policy Delivery</span><a class=self-link href=#policy-delivery></a></h2>
<p>The server delivers the policy to the user agent via an HTTP
response header or an HTML <a data-link-type=element href=http://www.w3.org/TR/html5/document-metadata.html#meta title=meta>meta</a> element. Servers are
informed that requests are subject to a policy via an HTTP request
header.</p>
<section>
<h3 class="heading settled heading" data-level=3.1 id=content-security-policy-header-field><span class=secno>3.1 </span><span class=content>
<code>Content-Security-Policy</code> Header Field
</span><a class=self-link href=#content-security-policy-header-field></a></h3>
<p>The <code><dfn data-dfn-type=dfn data-export="" id=content-security-policy>Content-Security-Policy<a class=self-link href=#content-security-policy></a></dfn></code> header field is
the preferred mechanism for delivering a policy.</p>
<pre>"Content-Security-Policy:" 1#<a data-link-type=dfn href=#policy-token title=policy-token>policy-token</a>
</pre>
<p>For example:</p>
<pre class=example>Content-Security-Policy: script-src 'self'
</pre>
<p>A server MAY send more than one HTTP header field named
<code>Content-Security-Policy</code> with a given resource
representation.</p>
<p>A server MAY send different <code>Content-Security-Policy</code>
header field values with different representations of the same
resource or with different resources.</p>
<p>Upon receiving an HTTP response containing at least one
<code>Content-Security-Policy</code> header field, the user agent
MUST <a data-link-type=dfn href=#enforce title=enforce>enforce</a> each of the policies contained in each such
header field.</p>
</section>
<section>
<h3 class="heading settled heading" data-level=3.2 id=content-security-policy-report-only-header-field><span class=secno>3.2 </span><span class=content>
<code>Content-Security-Policy-Report-Only</code> Header Field
</span><a class=self-link href=#content-security-policy-report-only-header-field></a></h3>
<p>The <code><dfn data-dfn-type=dfn data-export="" id=content-security-policy-report-only>Content-Security-Policy-Report-Only<a class=self-link href=#content-security-policy-report-only></a></dfn></code>
header field lets servers experiment with policies by monitoring (rather
than enforcing) a policy.</p>
<pre>"Content-Security-Policy-Report-Only:" 1#<a data-link-type=dfn href=#policy-token title=policy-token>policy-token</a>
</pre>
<p>For example, server operators might wish to develop their
security policy iteratively. The operators can deploy a report-only
policy based on their best estimate of how their site behaves:</p>
<pre class=example>Content-Security-Policy-Report-Only: script-src 'self'; report-uri /csp-report-endpoint/
</pre>
<p>If their site violates this policy the user agent will <a data-link-type=dfn href=#send-violation-reports title="send violation reports">send violation
reports</a> to the URI specified in the policy’s <a data-link-type=dfn href=#report-uri title=report-uri>report-uri</a>
directive, but allow the violating resources to load regardless. Once a site
has confidence that the policy is appropriate, they can start enforcing the
policy using the <code><a data-link-type=dfn href=#content-security-policy title=content-security-policy>Content-Security-Policy</a></code> header field.</p>
<p>A server MAY send more than one HTTP header field named
<code>Content-Security-Policy-Report-Only</code> with a given
resource representation.</p>
<p>A server MAY send different
<code>Content-Security-Policy-Report-Only</code> header field values
with different representations of the same resource or with different
resources.</p>
<p>Upon receiving an HTTP response containing at least one
<code>Content-Security-Policy-Report-Only</code> header field, the
user agent MUST <a data-link-type=dfn href=#monitor title=monitor>monitor</a> each of the policies
contained in each such header field.</p>
<p class=note>Note: The <code><a data-link-type=dfn href=#content-security-policy-report-only title=content-security-policy-report-only>Content-Security-Policy-Report-Only</a></code>
header is <em>not</em> supported inside a <code><a data-link-type=element href=http://www.w3.org/TR/html5/document-metadata.html#meta title=meta>meta</a></code>
element.</p>
</section>
<section>
<h3 class="heading settled heading" data-level=3.3 id=delivery-html-meta-element><span class=secno>3.3 </span><span class=content>
HTML <code><a data-link-type=element href=http://www.w3.org/TR/html5/document-metadata.html#meta title=meta>meta</a></code> Element
</span><a class=self-link href=#delivery-html-meta-element></a></h3>
<p>The server MAY supply a policy in an HTML <code><a data-link-type=element href=http://www.w3.org/TR/html5/document-metadata.html#meta title=meta>meta</a></code>
element with an <code><a data-link-type=element-attr href=http://www.w3.org/TR/html5/document-metadata.html#attr-meta-http-equiv title=http-equiv>http-equiv</a></code> attribute that
is a case insensitive match for the string
"<code>Content-Security-Policy</code>". For example:</p>
<pre class=example><meta http-equiv="Content-Security-Policy" content="script-src 'self'">
</pre>
Add the following entry to the
<a href=http://www.w3.org/TR/html5/document-metadata.html#pragma-directives>pragma directives</a>
for the <code><a data-link-type=element href=http://www.w3.org/TR/html5/document-metadata.html#meta title=meta>meta</a></code> element:
<dl>
<dt>
Content security policy
(<code>http-equiv="content-security-policy"</code>)
</dt>
<dd>
<ol>
<li>If the Document’s <code><a data-link-type=element href=http://www.w3.org/TR/html5/document-metadata.html#the-head-element title=head>head</a></code> element is
not an ancestor of the <code><a data-link-type=element href=http://www.w3.org/TR/html5/document-metadata.html#meta title=meta>meta</a></code> element, abort
these steps.</li>
<li>If the <code><a data-link-type=element href=http://www.w3.org/TR/html5/document-metadata.html#meta title=meta>meta</a></code> element lacks a
<code><a data-link-type=element-attr href=http://www.w3.org/TR/html5/document-metadata.html#attr-meta-content title=content>content</a></code> attribute, abort these
steps.</li>
<li>Let <var>policy</var> be the value of the
<code><a data-link-type=element-attr href=http://www.w3.org/TR/html5/document-metadata.html#attr-meta-content title=content>content</a></code> attribute of the
<code><a data-link-type=element href=http://www.w3.org/TR/html5/document-metadata.html#meta title=meta>meta</a></code> element.</li>
<li>Let <var>directive-set</var> be the result of
<a data-link-type=dfn href=#parse-the-policy title="parse the policy">parsing <var>policy</var></a>.</li>
<li>Remove all occurrences of <code><a data-link-type=dfn href=#reflected-xss title=reflected-xss>reflected-xss</a></code>,
<code><a data-link-type=dfn href=#report-uri title=report-uri>report-uri</a></code>, and <code><a data-link-type=dfn href=#sandbox title=sandbox>sandbox</a></code>
directives from <var>directive-set</var>.</li>
<li>Enforce each of the <a data-link-type=dfn href=#security-policy-directive title=directives>directives</a> in <var>directive-set</var>,
as <a href=#sec-directives>defined for each directive type</a>.</li>
</ol>
</dd>
</dl>
<p>Authors are <em>strongly encouraged</em> to place the
<code><a data-link-type=element href=http://www.w3.org/TR/html5/document-metadata.html#meta title=meta>meta</a></code> element as early in the document as
possible to reduce the risk of content injection before a protective
policy can be read and enforced.</p>
<p class=note>Note: A <a data-link-type=dfn href=#security-policy title=policy>policy</a> specified via a <code><a data-link-type=element href=http://www.w3.org/TR/html5/document-metadata.html#meta title=meta>meta</a></code>
element will be enforced along with any other policies active for the
protected resource, regardless of where they’re specified. The general
mechanism for determining the effect of enforcing multiple policies is
detailed in the <a data-section="" href=#enforcing-multiple-policies>§3.5 Enforcing multiple policies.</a>
section.</p>
<p class=note>Note: Modifications to the <code><a data-link-type=element-attr href=http://www.w3.org/TR/html5/document-metadata.html#attr-meta-content title=content>content</a></code>
attribute of a <code><a data-link-type=element href=http://www.w3.org/TR/html5/document-metadata.html#meta title=meta>meta</a></code> element after the
element has been parsed will be ignored.</p>
<p class=note>Note: The <code><a data-link-type=dfn href=#content-security-policy-report-only title=content-security-policy-report-only>Content-Security-Policy-Report-Only</a></code>
header is <em>not</em> supported inside a <code><a data-link-type=element href=http://www.w3.org/TR/html5/document-metadata.html#meta title=meta>meta</a></code>
element.</p>
</section>
<section>
<h3 class="heading settled heading" data-level=3.4 id=ch-csp-client-hint><span class=secno>3.4 </span><span class=content>The <code>CH-CSP</code> Client Hint</span><a class=self-link href=#ch-csp-client-hint></a></h3>
<p>The <code><dfn data-dfn-type=dfn data-noexport="" id=ch-csp>CH-CSP<a class=self-link href=#ch-csp></a></dfn></code> header field indicates that a particular
request is subject to a <a data-link-type=dfn href=#security-policy title=policy>policy</a>, and its value is defined by the
following ABNF grammar:</p>
<pre>"CH-CSP:" 1#<a data-link-type=dfn href=#hint-value title=hint-value>hint-value</a>
<dfn data-dfn-type=dfn data-noexport="" id=hint-value>hint-value<a class=self-link href=#hint-value></a></dfn> = *WSP "active"
</pre>
<p>If the user agent is <a data-link-type=dfn href=#monitor title=monitoring>monitoring</a> or <a data-link-type=dfn href=#enforce title=enforcing>enforcing</a> a <a data-link-type=dfn href=#security-policy title=policy>policy</a>
that includes directives whose value is a <a data-link-type=dfn href=#source-list0 title="source list">source list</a>, and whose
source list contains the <code>'unsafe-redirect'</code> source expression,
then the user agent MUST send a header field named <code>CH-CSP</code>
along with requests for resources whose <a data-link-type=dfn href=#origin title=origin>origin</a> <em>does not</em>
match the <a data-link-type=dfn href=#protected-resource title="protected resource">protected resource</a>’s origin. The value of this header MUST
be <code>active</code>.</p>
<p>The user agent MAY choose to send this header only if the request is for a
resource type which the active policy would effect. That is, given a policy
of <code>img-src example.com 'unsafe-redirect'</code>, the user agent
would send <code>CH-CSP: active</code> along with requests for images, but
might choose not to send the header with requests for script.</p>
<p class=note>Note: The central reason for including this header is that it hints to a
server that information about redirects might be leaked as a side-effect
of a page’s active policy. If this header is present, a server might decline
to redirect a logged-out user from <code>example.com</code> to
<code>accounts.example.com</code>, for example, as a malicious embedder
might otherwise be able to determine the user’s logged-in status.</p>
</section>
<section>
<h3 class="heading settled heading" data-level=3.5 id=enforcing-multiple-policies><span class=secno>3.5 </span><span class=content>Enforcing multiple policies.</span><a class=self-link href=#enforcing-multiple-policies></a></h3>
<p><em>This section is not normative.</em></p>
<p>The above sections note that when multiple policies are present,
each must be enforced or reported, according to its type. An example
will help clarify how that ought to work in practice. The behavior of
an <code>XMLHttpRequest</code> might seem unclear given a site
that, for whatever reason, delivered the following HTTP headers:</p>
<pre class=example>Content-Security-Policy: <a data-link-type=dfn href=#default-src title=default-src>default-src</a> 'self' http://example.com http://example.net;
<a data-link-type=dfn href=#connect-src title=connect-src>connect-src</a> 'none';
Content-Security-Policy: <a data-link-type=dfn href=#connect-src title=connect-src>connect-src</a> http://example.com/;
<a data-link-type=dfn href=#script-src title=script-src>script-src</a> http://example.com/
</pre>
<p>Is a connection to <code>example.com</code> allowed or not? The
short answer is that the connection is not allowed. Enforcing both
policies means that a potential connection would have to pass through
both unscathed. Even though the second policy would allow this
connection, the first policy contains <code><a data-link-type=dfn href=#connect-src title=connect-src>connect-src</a>
'none'</code>, so its enforcement blocks the connection. The impact is
that adding additional policies to the list of policies to enforce can
only further restrict the capabilities of the protected resource.</p>
<p>To demonstrate that further, consider a script tag on this page.
The first policy would lock scripts down to <code>'self'</code>,
<code>http://example.com</code> and <code>http://example.net</code>
via the <code><a data-link-type=dfn href=#default-src title=default-src>default-src</a></code> directive. The second, however,
would only allow script from <code>http://example.com/</code>. Script
will only load if it meets both policy’s criteria: in this case, the only
origin that can match is <code>http://example.com</code>, as both
policies allow it.</p>
</section>
<section>
<h3 class="heading settled heading" data-level=3.6 id=which-policy-applies><span class=secno>3.6 </span><span class=content>Policy applicability</span><a class=self-link href=#which-policy-applies></a></h3>
<p><em>This section is not normative.</em></p>
<p>Policies are associated with an <a data-link-type=dfn href=#protected-resource title="protected resource">protected resource</a>, and
<a data-link-type=dfn href=#enforce title=enforce>enforced</a> or <a data-link-type=dfn href=#monitor title=monitored>monitored</a> for for that resource.
If a resource does not create a new execution context (for example, when
including a script, image, or stylesheet into a document), then any policies
delivered with that resource are discarded without effect. Its execution is
subject to the policy or policies of the including context. The following
table outlines examples of these relationships:</p>
<table>
<thead>
<tr>
<th colspan=2>Resource Type</th>
<th>What <a data-link-type=dfn href=#security-policy title=policy>policy</a> applies?</th>
<tr>
</thead>
<tbody>
<tr class=section>
<th rowspan=2>Top-level Contexts</th>
<td>HTML as a new, top-level browsing context</td>
<td>The policy delivered with the resource</td>
</tr>
<tr>
<td>SVG, as a top-level document</td>
<td>Policy delivered with the resource</td>
</tr>
<tr class=section>
<th rowspan=3>Embedded Contexts</th>
<td>
Any resource included via <a data-link-type=element href=http://www.w3.org/TR/html5/embedded-content-0.html#the-iframe-element title=iframe>iframe</a>,
<a data-link-type=element href=http://www.w3.org/TR/html5/embedded-content-0.html#the-object-element title=object>object</a>, or <a data-link-type=element href=http://www.w3.org/TR/html5/embedded-content-0.html#the-embed-element title=embed>embed</a>
</td>
<td>
The policy of the embedding resource controls <em>what</em> may be
embedded. The embedded resource, however, is controlled by the
policy delivered with the resource, or the policy of the embedding
resource if the embedded resource is a <a data-link-type=dfn href=#globally-unique-identifier title="globally unique identifier">globally unique
identifier</a> (or a <a data-link-type=element-attr href=http://www.w3.org/TR/html5/embedded-content-0.html#attr-iframe-srcdoc title=srcdoc>srcdoc</a> frame).
</td>
</tr>
<tr>
<td>SVG, as an embedded document</td>
<td>
The policy delivered with the resource, or policy of the creating
context if created from a <a data-link-type=dfn href=#globally-unique-identifier title="globally unique identifier">globally unique identifier</a>.
</td>
</tr>
<tr>
<td>
JavaScript, as a Worker, Shared Worker or Service Worker
</td>
<td>
The policy delivered with the resource, or policy of the creating
context if created from a <a data-link-type=dfn href=#globally-unique-identifier title="globally unique identifier">globally unique identifier</a>
</td>
</tr>
<tr class=section>
<th rowspan=7>Subresources</th>
<td>SVG, inlined via <a data-link-type=element href=http://www.w3.org/TR/svg2/struct.html#elementdef-svg title=svg>svg</a></td>
<td>Policy of the including context</td>
</tr>
<tr>
<td>SVG, as a resource document</td>
<td>Policy of the including context</td>
</tr>
<tr>
<td>HTML via XMLHttpRequest</td>
<td>Policy of the context that performed the fetch</td>
</tr>
<tr>
<td>Image via <a data-link-type=element href=http://www.w3.org/TR/html5/embedded-content-0.html#the-img-element title=img>img</a> element</td>
<td>Policy of the including context</td>
</tr>
<tr>
<td>JavaScript via a <a data-link-type=element href=http://www.w3.org/TR/html5/scripting-1.html#script title=script>script</a> element</td>
<td>Policy of the including context</td>
</tr>
<tr>
<td>SVG, via <a data-link-type=element href=http://www.w3.org/TR/html5/embedded-content-0.html#the-img-element title=img>img</a></td>
<td>No policy; should be just as safe as JPG</td>
</tr>
<tr>
<td>SVG, as a WebFont</td>
<td>No policy; should be just as safe as WOFF</td>
</tr>
</tbody>
</table>
</section>
</section>
<section>
<h2 class="heading settled heading" data-level=4 id=syntax-and-algorithms><span class=secno>4 </span><span class=content>Syntax and Algorithms</span><a class=self-link href=#syntax-and-algorithms></a></h2>
<section>
<h3 class="heading settled heading" data-level=4.1 id=policy-syntax><span class=secno>4.1 </span><span class=content>Policy Syntax</span><a class=self-link href=#policy-syntax></a></h3>
<p>A Content Security Policy consists of a U+003B SEMICOLON
(<code>;</code>) delimited list of directives. Each <a data-link-type=dfn href=#security-policy-directive title=directive>directive</a>
consists of a <a data-link-type=dfn href=#directive-name0 title="directive name">directive name</a> and (optionally) a
<a data-link-type=dfn href=#directive-value0 title="directive value">directive value</a>, defined by the following ABNF:</p>
<pre><dfn data-dfn-type=dfn data-noexport="" id=policy-token>policy-token<a class=self-link href=#policy-token></a></dfn> = [ <a data-link-type=dfn href=#directive-token title=directive-token>directive-token</a> *( ";" [ <a data-link-type=dfn href=#directive-token title=directive-token>directive-token</a> ] ) ]
<dfn data-dfn-type=dfn data-noexport="" id=directive-token>directive-token<a class=self-link href=#directive-token></a></dfn> = *WSP [ <a data-link-type=dfn href=#directive-name title=directive-name>directive-name</a> [ WSP <a data-link-type=dfn href=#directive-value title=directive-value>directive-value</a> ] ]
<dfn data-dfn-type=dfn data-noexport="" id=directive-name>directive-name<a class=self-link href=#directive-name></a></dfn> = 1*( ALPHA / DIGIT / "-" )
<dfn data-dfn-type=dfn data-noexport="" id=directive-value>directive-value<a class=self-link href=#directive-value></a></dfn> = *( WSP / <VCHAR except ";" and ","> )
</pre>
<section>
<h4 class="heading settled heading" data-level=4.1.1 id=policy-parsing><span class=secno>4.1.1 </span><span class=content>Parsing Policies</span><a class=self-link href=#policy-parsing></a></h4>
<p>To <dfn data-dfn-type=dfn data-noexport="" id=parse-the-policy>parse the policy<a class=self-link href=#parse-the-policy></a></dfn> <var>policy</var>, the user agent MUST
use an algorithm equivalent to the following:</p>
<ol>
<li>Let the <var>set of directives</var> be the empty set.</li>
<li>For each non-empty token returned by
<a data-link-spec=HTML5 data-link-type=dfn href=http://www.w3.org/TR/html5/infrastructure.html#strictly-split-a-string title="strictly split a string">strictly splitting</a>
the string <var>policy</var> on the character U+003B SEMICOLON
(<code>;</code>):
<ol>
<li><a data-link-spec=HTML5 data-link-type=dfn href=http://www.w3.org/TR/html5/infrastructure.html#skip-whitespace title="skip whitespace">Skip whitespace</a>.</li>
<li><a data-link-spec=HTML5 data-link-type=dfn href=http://www.w3.org/TR/html5/infrastructure.html#collect-a-sequence-of-characters title="collect a sequence of characters">Collect a sequence of characters</a> that are
not <a data-link-spec=HTML5 data-link-type=dfn href=http://www.w3.org/TR/html5/infrastructure.html#space-character title="space characters">space characters</a>. The collected characters
are the <var>directive name</var>.</li>
<li>If there are characters remaining in <var>token</var>,
skip ahead exactly one character (which must be a
<a data-link-spec=HTML5 data-link-type=dfn href=http://www.w3.org/TR/html5/infrastructure.html#space-character title="space character">space character</a>).</li>
<li>The remaining characters in <var>token</var> (if any) are
the <var>directive value</var>.</li>
<li>If the <var>set of directives</var> already contains a
directive whose name is a case insensitive match for
<var>directive name</var>, ignore this instance of the directive
and continue to the next token.</li>
<li>Add a <var>directive</var> to the <var>set of
directives</var> with name <var>directive name</var> and value
<var>directive value</var>.</li>
</ol>
</li>
<li>Return the <var>set of directives</var>.
</ol>
</section>
</section>
<section>
<h3 class="heading settled heading" data-level=4.2 id=source-list-syntax><span class=secno>4.2 </span><span class=content>Source List Syntax</span><a class=self-link href=#source-list-syntax></a></h3>
<p>Many CSP directives use a value consisting of a <dfn data-dfn-type=dfn data-noexport="" id=source-list0>source
list<a class=self-link href=#source-list0></a></dfn>, defined in the ABNF grammar below.</p>
<p>Each <dfn data-dfn-type=dfn data-noexport="" id=source-expression0>source expression<a class=self-link href=#source-expression0></a></dfn> in the source list represents a
location from which content of the specified type can be retrieved.
For example, the source expression <code>'none'</code> represents
the empty set of URIs, and the source expression
<code>'unsafe-inline'</code> represents content supplied inline in the
resource itself.</p>
<pre><dfn data-dfn-type=dfn data-noexport="" id=source-list>source-list<a class=self-link href=#source-list></a></dfn> = *WSP [ <a data-link-type=dfn href=#source-expression title=source-expression>source-expression</a> *( 1*WSP <a data-link-type=dfn href=#source-expression title=source-expression>source-expression</a> ) *WSP ]
/ *WSP "'none'" *WSP
<dfn data-dfn-type=dfn data-noexport="" id=source-expression>source-expression<a class=self-link href=#source-expression></a></dfn> = <a data-link-type=dfn href=#scheme-source title=scheme-source>scheme-source</a> / <a data-link-type=dfn href=#host-source title=host-source>host-source</a> / <a data-link-type=dfn href=#keyword-source title=keyword-source>keyword-source</a> / <a data-link-type=dfn href=#nonce-source title=nonce-source>nonce-source</a> / <a data-link-type=dfn href=#hash-source title=hash-source>hash-source</a>
<dfn data-dfn-type=dfn data-noexport="" id=scheme-source>scheme-source<a class=self-link href=#scheme-source></a></dfn> = <a data-link-type=dfn href=#scheme-part title=scheme-part>scheme-part</a> ":"
<dfn data-dfn-type=dfn data-noexport="" id=host-source>host-source<a class=self-link href=#host-source></a></dfn> = [ <a data-link-type=dfn href=#scheme-part title=scheme-part>scheme-part</a> "://" ] <a data-link-type=dfn href=#host-part title=host-part>host-part</a> [ <a data-link-type=dfn href=#port-part title=port-part>port-part</a> ] [ <a data-link-type=dfn href=#path-part title=path-part>path-part</a> ]
<dfn data-dfn-type=dfn data-noexport="" id=keyword-source>keyword-source<a class=self-link href=#keyword-source></a></dfn> = "'self'" / "'unsafe-inline'" / "'unsafe-eval'" / "'unsafe-redirect'"
<dfn data-dfn-type=dfn data-noexport="" id=base64-value>base64-value<a class=self-link href=#base64-value></a></dfn> = 1*( ALPHA / DIGIT / "+" / "/" )*2( "=" )
<dfn data-dfn-type=dfn data-noexport="" id=nonce-value>nonce-value<a class=self-link href=#nonce-value></a></dfn> = <a data-link-type=dfn href=#base64-value title=base64-value>base64-value</a>
<dfn data-dfn-type=dfn data-noexport="" id=hash-value>hash-value<a class=self-link href=#hash-value></a></dfn> = <a data-link-type=dfn href=#base64-value title=base64-value>base64-value</a>
<dfn data-dfn-type=dfn data-noexport="" id=nonce-source>nonce-source<a class=self-link href=#nonce-source></a></dfn> = "'nonce-" <a data-link-type=dfn href=#nonce-value title=nonce-value>nonce-value</a> "'"
<dfn data-dfn-type=dfn data-noexport="" id=hash-algo>hash-algo<a class=self-link href=#hash-algo></a></dfn> = "sha256" / "sha384" / "sha512"
<dfn data-dfn-type=dfn data-noexport="" id=hash-source>hash-source<a class=self-link href=#hash-source></a></dfn> = "'" <a data-link-type=dfn href=#hash-algo title=hash-algo>hash-algo</a> "-" <a data-link-type=dfn href=#base64-value title=base64-value>base64-value</a> "'"
<dfn data-dfn-type=dfn data-noexport="" id=scheme-part>scheme-part<a class=self-link href=#scheme-part></a></dfn> = <scheme production from <a href=http://tools.ietf.org/html/rfc3986#section-3.1>RFC 3986, section 3.1</a>>
<dfn data-dfn-type=dfn data-noexport="" id=host-part>host-part<a class=self-link href=#host-part></a></dfn> = "*" / [ "*." ] 1*<a data-link-type=dfn href=#host-char title=host-char>host-char</a> *( "." 1*<a data-link-type=dfn href=#host-char title=host-char>host-char</a> )
<dfn data-dfn-type=dfn data-noexport="" id=host-char>host-char<a class=self-link href=#host-char></a></dfn> = ALPHA / DIGIT / "-"
<dfn data-dfn-type=dfn data-noexport="" id=path-part>path-part<a class=self-link href=#path-part></a></dfn> = <path production from <a href=http://tools.ietf.org/html/rfc3986#section-3.3>RFC 3986, section 3.3</a>>
<dfn data-dfn-type=dfn data-noexport="" id=port-part>port-part<a class=self-link href=#port-part></a></dfn> = ":" ( 1*DIGIT / "*" )
</pre>
<p>If the policy contains a <code><a data-link-type=dfn href=#nonce-source title=nonce-source>nonce-source</a></code> expression, the
server MUST generate a fresh value for the <code><a data-link-type=dfn href=#nonce-value title=nonce-value>nonce-value</a></code>
directive at random and independently each time it transmits a policy.
This requirement ensures that the <code><a data-link-type=dfn href=#nonce-value title=nonce-value>nonce-value</a></code> is
difficult for an attacker to predict.</p>
<p>The <code><a data-link-type=dfn href=#host-char title=host-char>host-char</a></code> production intentionally contains only
ASCII characters; internationalized domain names cannot be entered
directly into a policy string, but instead MUST be Punycode-encoded
<a data-biblio-type=normative data-link-type=biblio href=#biblio-rfc3492 title=biblio-rfc3492>[RFC3492]</a>. For example, the domain <code>üüüüüü.de</code> would be
encoded as <code>xn--tdaaaaaa.de</code>.</p>
<section>
<h4 class="heading settled heading" data-level=4.2.1 id=source-list-parsing><span class=secno>4.2.1 </span><span class=content>Parsing Source Lists</span><a class=self-link href=#source-list-parsing></a></h4>
<p>To <dfn data-dfn-type=dfn data-noexport="" id=parse-a-source-list>parse a source list<a class=self-link href=#parse-a-source-list></a></dfn>
<var>source list</var>, the user agent MUST use an algorithm
equivalent to the following:</p>
<ol>
<li><a data-link-spec=HTML5 data-link-type=dfn href=http://www.w3.org/TR/html5/infrastructure.html#strip-leading-and-trailing-whitespace title="strip leading and trailing whitespace">Strip leading and trailing whitespace</a> from
<var>source list</var>.</li>
<li>If <var>source list</var> is a case insensitive match
for the string <code>'none'</code> (including the quotation
marks), return the empty set.</li>
<li>Let <var>set of source expressions</var> be the empty
set.</li>
<li>For each token returned by
<a data-link-spec=HTML5 data-link-type=dfn href=http://www.w3.org/TR/html5/infrastructure.html#split-a-string-on-spaces title="split a string on spaces">splitting <var>source
list</var> on spaces</a>, if the token matches the grammar for
<code><a data-link-type=dfn href=#source-expression title=source-expression>source-expression</a></code>, add the token to the <var>set
of source expressions</var>.</li>
<li>Return the <var>set of source expressions</var>.</li>
</ol>
<p class=note>Note: Characters like U+003B SEMICOLON (<code>;</code>) and
U+002C COMMA (<code>,</code>) cannot appear in source expressions
directly: if you’d like to include these characters in a source
expression, they must be <a data-link-spec=HTML5 data-link-type=dfn href=http://www.w3.org/TR/html5/infrastructure.html#percent-encode title="percent encode">percent
encoded</a> as <code>%3B</code> and <code>%2C</code> respectively.</p>
</section>
<section>
<h4 class="heading settled heading" data-level=4.2.2 id=match-source-expression><span class=secno>4.2.2 </span><span class=content>Matching Source Expressions</span><a class=self-link href=#match-source-expression></a></h4>
<p>A URI is said to <dfn data-dfn-type=dfn data-noexport="" id=match-a-source-expression>match a source expression<a class=self-link href=#match-a-source-expression></a></dfn> if the following
algorithm returns <em>does match</em>:</p>
<ol>
<li>Normalize the URI according to
<a href=http://tools.ietf.org/html/rfc3986#section-6>Section 6 of
RFC3986</a>.</li>
<li>If the source expression a consists of a single U+002A ASTERISK
character (<code>*</code>), and the URI’s scheme is not of a type
designating a <a data-link-type=dfn href=#globally-unique-identifier title="globally unique identifier">globally unique identifier</a>, (such as
<code>blob:</code>, <code>data:</code>, or <code>filesystem:</code>)
then return <em>does match</em>.</li>
<li>If the source expression matches the grammar for
<code><a data-link-type=dfn href=#scheme-source title=scheme-source>scheme-source</a></code>:
<ol>
<li>If the URI’s scheme is a case-insensitive match for the
source expression’s <code><a data-link-type=dfn href=#scheme-part title=scheme-part>scheme-part</a></code>, return
<em>does match</em>.</li>
<li>Otherwise, return <em>does not match</em>.</li>
</ol>
</li>
<li>If the source expression matches the grammar for
<code><a data-link-type=dfn href=#host-source title=host-source>host-source</a></code>:
<ol>
<li>If the URI does <strong>not</strong> contain a host, then
return <em>does not match</em>.</li>
<li>Let <var>uri-scheme</var>, <var>uri-host</var>, and
<var>uri-port</var> be the scheme, host, and port of the URI,
respectively. If the URI does not have a port, then let
<var>uri-port</var> be the default port for
<var>uri-scheme</var>. Let <var>uri-path</var> be
the path of the URI after
<a data-link-spec=HTML5 data-link-type=dfn href=http://www.w3.org/TR/html5/infrastructure.html#percent-decode title="percent decode">decoding
percent-encoded characters</a>. If the URI does not have a
path, then let <var>uri-path</var> be the U+002F SOLIDUS
character (<code>/</code>).</li>
<li>If the source expression has a <code><a data-link-type=dfn href=#scheme-part title=scheme-part>scheme-part</a></code>
that is not a case insensitive match for <var>uri-scheme</var>,
then return <em>does not match</em>.</li>
<li>If the source expression does <strong>not</strong> have a
scheme, return <em>does not match</em> if
<ol>
<li>the scheme of the protected resource’s URI is a case
insensitive match for <code>HTTP</code>, and
<var>uri-scheme</var> is <strong>not</strong> a case
insensitive match for either <code>HTTP</code> or
<code>HTTPS</code></li>
<li>the scheme of the protected resource’s URI is
<strong>not</strong> a case insensitive match for
<code>HTTP</code>, and <var>uri-scheme</var> is
<strong>not</strong> a case insensitive match
for the scheme of the protected resource’s URI.</li>
</ol>
</li>
<li>If the first character of the source expression’s
<code><a data-link-type=dfn href=#host-part title=host-part>host-part</a></code> is an U+002A ASTERISK character
(<code>*</code>) and the remaining characters, including the
leading U+002E FULL STOP character (<code>.</code>), are not a
case insensitive match for the rightmost characters of
<var>uri-host</var>, then return <em>does not match</em>.</li>
<li>If the first character of the source expression’s
<code><a data-link-type=dfn href=#host-part title=host-part>host-part</a></code> is <em>not</em> an U+002A ASTERISK
character (<code>*</code>) and <var>uri-host</var> is not a
case insensitive match for the source expression’s
<code><a data-link-type=dfn href=#host-part title=host-part>host-part</a></code>, then return <em>does not
match</em>.</li>
<li>If the source expression does <strong>not</strong> contain
a <code>port-part</code> and <var>uri-port</var> is not the
default port for <var>uri-scheme</var>, then return <em>does not
match</em>.</li>
<li>If the source expression does contain a
<code>port-part</code>, then return <em>does not match</em> if
<ol>
<li><code><a data-link-type=dfn href=#port-part title=port-part>port-part</a></code> does <strong>not</strong>
contain an U+002A ASTERISK character (<code>*</code>),
and</li>
<li><code><a data-link-type=dfn href=#port-part title=port-part>port-part</a></code> does <strong>not</strong>
represent the same number as <var>uri-port</var>.</li>
</ol>
</li>
<li>If the source expression contains a non-empty
<code><a data-link-type=dfn href=#path-part title=path-part>path-part</a></code>, and the URI is <em>not</em> the
result of a redirect, then:
<ol>
<li>Let <var>decoded-path</var> be the result of
<a data-link-spec=HTML5 data-link-type=dfn href=http://www.w3.org/TR/html5/infrastructure.html#percent-decode title="percent decode">decoding
<code>path-part</code>’s percent-encoded characters</a>.</li>
<li>If the final character of <var>decoded-path</var> is
the U+002F SOLIDUS character (<code>/</code>), and
<var>decoded-path</var> is not a prefix of
<var>uri-path</var>, then return <em>does not
match</em>.</li>
<li>If the final character of <var>decoded-path</var> is
not the the U+002F SOLIDUS character (<code>/</code>),
and <var>decoded-path</var> is not an exact match for
<var>uri-path</var> then return <em>does not
match</em>.</li>
</ol>
</li>
<li>Otherwise, return <em>does match</em>.</li>
</ol>
</li>
<li>If the source expression is a case insensitive
match for <code>'self'</code> (including the quotation marks),
then:
<ol>
<li>Return <em>does match</em> if the URI has the same scheme,
host, and port as the protected resource’s URI (using the
default port for the appropriate scheme if either or both URIs
are missing ports).</li>
</ol>
</li>
<li>Otherwise, return <em>does not match</em>.</li>
</ol>
<p>A URI is said to <dfn data-dfn-type=dfn data-noexport="" id=match-a-source-list>match a source list<a class=self-link href=#match-a-source-list></a></dfn> if the following
conditions are met:</p>
<ol>
<li>
The URI <a data-link-type=dfn href=#match-a-source-expression title="match a source expression">matches at least one
source expression</a> in the set of source expressions obtained by
<a data-link-type=dfn href=#parse-a-source-list title="parse a source list">parsing the source list</a>.
</li>