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<h1>Content Security Policy Level 3</h1>
<pre class="metadata">
Status: WD
ED: https://w3c.github.io/webappsec-csp/
TR: https://www.w3.org/TR/CSP3/
Shortname: CSP3
Level: None
Issue Tracking: Github https://github.com/w3c/webappsec-csp/issues/new
Editor: Mike West 56384, Google Inc., mkwst@google.com
Editor: Antonio Sartori 124875, Google Inc., antoniosartori@google.com
Group: webappsec
Abstract:
This document defines a mechanism by which web developers can control the
resources which a particular page can fetch or execute, as well as a number
of security-relevant policy decisions.
Indent: 2
Version History: https://github.com/w3c/webappsec-csp/commits/main/index.src.html
Boilerplate: feedback-header off
!Participate: <a href="https://github.com/w3c/webappsec-csp/issues/new">File an issue</a> (<a href="https://github.com/w3c/webappsec-csp/issues">open issues</a>)
!Tests: <a href=https://github.com/web-platform-tests/wpt/tree/master/content-security-policy>web-platform-tests content-security-policy/</a> (<a href=https://github.com/web-platform-tests/wpt/labels/content-security-policy>ongoing work</a>)
Markup Shorthands: css off, markdown on
At Risk: The [[#is-element-nonceable]] algorithm.
</pre>
<pre class="link-defaults">
spec:dom; type:interface; text:Document
spec:html
type: dfn
text: plugin document
text: fallback base url
text: duplicate-attribute
type: element
text: a
text: link
text: script
text: style
type: element-attr
text: ping
spec:fetch
type: dfn
text: main fetch
text: http-network fetch
text: http fetch
text: response; for: /
spec:url
type: dfn
text: default port
text: base url
type:interface;
text:URL
spec:cssom
type: dfn
text: insert a css rule
text: parse a css declaration block
text: parse a css rule
text: parse a group of selectors
spec:css-cascade
type: at-rule
text: @import
spec:infra;
type:dfn;
text:string; for: /
text:list; for: /
text:set; for: /
text:append; for: set
text:empty; for: set
text:strictly split a string
</pre>
<pre class="anchors">
spec: RFC6454; urlPrefix: https://tools.ietf.org/html/rfc6454
type: dfn
text: the same; url: section-5
spec: ECMA262; urlPrefix: https://tc39.github.io/ecma262
type: dfn
text: realm
type: method
text: HostEnsureCanCompileStrings(); url: sec-hostensurecancompilestrings
text: eval(); url: sec-eval-x
text: Function(); url: sec-function-objects
spec: FETCH; urlPrefix: https://fetch.spec.whatwg.org/
type: dfn
for: request
text: target browsing context; url: concept-request-target-browsing-context
spec: MIX; urlPrefix: https://www.w3.org/TR/mixed-content/
type: dfn; text: block-all-mixed-content
spec: RFC3986; urlPrefix: https://tools.ietf.org/html/rfc3986
type: grammar
text: path-absolute; url: section-3.3
text: scheme; url: section-3.1
text: IPv4address; url: section-3.2.2
text: uri-reference; url: section-4.1
spec: RFC4648; urlPrefix: https://tools.ietf.org/html/rfc4648
type: dfn
text: base64 encoding; url: section-4
text: base64url encoding; url: section-5
spec: RFC5234; urlPrefix: https://tools.ietf.org/html/rfc5234
type: grammar
text: ALPHA; url: appendix-B.1
text: DIGIT; url: appendix-B.1
text: VCHAR; url: appendix-B.1
spec: RFC5890; urlPrefix: https://tools.ietf.org/html/rfc5890
type: dfn
text: label; url: section-2.2
spec: RFC9110; urlPrefix: https://tools.ietf.org/html/rfc9110
type: grammar
text: OWS; url: section-5.6.3
text: token; url: section-5.6.2
spec: RFC7231; urlPrefix: https://tools.ietf.org/html/rfc7231
type: dfn
url: section-3
text: resource representation
text: representation
spec: REPORTING; urlPrefix: https://w3c.github.io/reporting/
type: dfn
text: group
text: queue report; url: queue-report
text: report type
text: visible to reportingobservers
spec: SHA2; urlPrefix: https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.180-4.pdf
type: dfn
text: SHA-256; url: #
text: SHA-384; url: #
text: SHA-512; url: #
spec: HTML; urlPrefix: https://html.spec.whatwg.org/
type: dfn
for: script
text: "parser-inserted"
text: origin; url: concept-origin
text: browsing context; url: browsing-context
text: content security policy state; url: attr-meta-http-equiv-content-security-policy
text: create and initialize a new document object; url: initialise-the-document-object
text: initializing a new Document object; url: initialise-the-document-object
text: prepare the script element; url: prepare-the-script-element
spec: INFRA; urlPrefix: https://infra.spec.whatwg.org/
type: grammar
text: ASCII whitespace; url: ascii-whitespace
text: INFRA; url: #
spec: WebAssembly-js-api; urlPrefix: https://webassembly.github.io/spec/js-api/
type: method
text: new WebAssembly.Module(); url: #dom-module-module
text: WebAssembly.compile(); url: #dom-webassembly-compile
text: WebAssembly.instantiate(); url: #dom-webassembly-instantiate
text: HostEnsureCanCompileWasmBytes(); url:#dom-host-ensure-can-compile-wasm-bytes
spec: WebAssembly-web-api-api; urlPrefix: https://webassembly.github.io/spec/web-api/
type: method
text: WebAssembly.compileStreaming(); url: #dom-webassembly-compilestreaming
text: WebAssembly.instantiateStreaming(); url: #dom-webassembly-instantiatestreaming
type: exception
text: WebAssembly.CompileError; url: #exceptiondef-compileerror
spec: WebRTC; urlPrefix: https://www.w3.org/TR/webrtc/
type:dfn
text: administratively-prohibited; url: #dfn-administratively-prohibited
</pre>
<pre class="biblio">
{
"HTML-DESIGN": {
"authors": [ "Anne Van Kesteren", "Maciej Stachowiak" ],
"href": "https://www.w3.org/TR/html-design-principles/",
"title": "HTML Design Principles",
"publisher": "W3C"
},
"ECMA262": {
"authors": [ "Brian Terlson", "Allen Wirfs-Brock" ],
"href": "https://tc39.github.io/ecma262/",
"title": "ECMAScript® Language Specification",
"publisher": "ECMA"
},
"REPORTING": {
"href": "https://wicg.github.io/reporting/",
"title": "Reporting API",
"authors": [ "Ilya Gregorik", "Mike West" ]
},
"TIMING": {
"href": "https://www.contextis.com/media/downloads/Pixel_Perfect_Timing_Attacks_with_HTML5_Whitepaper.pdf",
"title": "Pixel Perfect Timing Attacks with HTML5",
"authors": [ "Paul Stone" ],
"publisher": "Context Information Security"
},
"H5SC3": {
"href": "https://github.com/cure53/XSSChallengeWiki/wiki/H5SC-Minichallenge-3:-%22Sh*t,-it%27s-CSP!%22",
"title": "H5SC Minichallenge 3: \"Sh*t, it's CSP!\"",
"authors": [ "Mario Heiderich" ],
"publisher": "Cure53"
},
"CSS-ABUSE": {
"href": "https://scarybeastsecurity.blogspot.com/2009/12/generic-cross-browser-cross-domain.html",
"title": "Generic cross-browser cross-domain theft",
"authors": [ "Chris Evans" ],
"date": "28 December 2009"
},
"FILEDESCRIPTOR-2015": {
"href": "https://blog.innerht.ml/csp-2015/#danglingmarkupinjection",
"title": "CSP 2015",
"authors": [ "filedescriptor" ],
"date": "23 November 2015"
},
"LONG-LIVE-CSP": {
"href": "https://dl.acm.org/doi/10.1145/2976749.2978363",
"title": "CSP Is Dead, Long Live CSP! On the Insecurity of Whitelists and the Future of Content Security Policy",
"authors": [ "Lukas Weichselbaum", "Michele Spagnuolo", "Sebastian Lekies", "Artur Janc" ],
"date": "24 October 2016"
},
"WEBDEV-STRICTCSP": {
"href": "https://web.dev/strict-csp/",
"title": "Mitigate cross-site scripting (XSS) with a strict Content Security Policy (CSP)",
"authors": [ "Lukas Weichselbaum" ],
"date": "15 March 2021"
}
}
</pre>
<style>
ul.toc ul ul ul {
margin: 0 0 0 2em;
}
ul.toc ul ul ul span.secno {
margin-left: -9em;
}
a[href^="http:"]:after {
color: red;
content: "🔓";
}
.wip {
margin: 1em auto;
background: #FCFAEE;
border: 0.5em;
border-left-style: solid;
border-color: #E0CB52;
padding: 0.5em;
}
.wip::before {
content: "Work In Progress: ";
display: block;
color: #827017;
}
section.wip {
padding-left: 2em;
}
</style>
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<section>
<h2 id="intro">Introduction</h2>
<em>This section is not normative.</em>
This document defines <dfn export>Content Security Policy</dfn> (CSP), a tool
which developers can use to lock down their applications in various ways,
mitigating the risk of content injection vulnerabilities such as cross-site scripting, and
reducing the privilege with which their applications execute.
CSP is not intended as a first line of defense against content injection
vulnerabilities. Instead, CSP is best used as defense-in-depth. It reduces
the harm that a malicious injection can cause, but it is not a replacement for
careful input validation and output encoding.
This document is an iteration on Content Security Policy Level 2, with the
goal of more clearly explaining the interactions between CSP, HTML, and Fetch
on the one hand, and providing clear hooks for modular extensibility on the
other. Ideally, this will form a stable core upon which we can build new
functionality.
<h3 id="examples">Examples</h3>
<h4 id="example-basic">Control Execution</h4>
<div class="example">
MegaCorp Inc's developers want to protect themselves against cross-site
scripting attacks. They can mitigate the risk of script injection by
ensuring that their trusted CDN is the only origin from which script can
load and execute. Moreover, they wish to ensure that no plugins can
execute in their pages' contexts. The following policy has that effect:
<pre>
<a http-header>Content-Security-Policy</a>: script-src https://cdn.example.com/scripts/; object-src 'none'
</pre>
</div>
<h3 id="goals">Goals</h3>
Content Security Policy aims to do to a few related things:
1. Mitigate the risk of content-injection attacks by giving developers
fairly granular control over
* The resources which can be requested (and subsequently embedded or
executed) on behalf of a specific {{Document}} or {{Worker}}
* The execution of inline script
* Dynamic code execution (via {{eval()}} and similar constructs)
* The application of inline style
2. Mitigate the risk of attacks which require a resource to be embedded
in a malicious context (the "Pixel Perfect" attack described in
[[TIMING]], for example) by giving developers granular control over the
origins which can embed a given resource.
3. Provide a policy framework which allows developers to reduce the privilege
of their applications.
4. Provide a reporting mechanism which allows developers to detect flaws
being exploited in the wild.
<h3 id="changes-from-level-2">Changes from Level 2</h3>
This document describes an evolution of the Content Security Policy Level 2
specification [[CSP2]]. The following is a high-level overview of the changes:
1. The specification has been rewritten from the ground up in terms of the
[[FETCH]] specification, which should make it simpler to integrate CSP's
requirements and restrictions with other specifications (and with
Service Workers in particular).
2. The `child-src` model has been substantially altered:
1. The `frame-src` directive, which was deprecated in CSP Level
2, has been undeprecated, but continues to defer to `child-src` if
not present (which defers to `default-src` in turn).
2. A `worker-src` directive has been added, deferring to `child-src`
if not present (which likewise defers to `script-src` and
eventually `default-src`).
3. The URL matching algorithm now treats insecure schemes and ports as
matching their secure variants. That is, the source expression
`http://example.com:80` will match both `http://example.com:80` and
`https://example.com:443`.
Likewise, `'self'` now matches `https:` and `wss:` variants of the page's
origin, even on pages whose scheme is `http`.
4. Violation reports generated from inline script or style will now report
"`inline`" as the blocked resource. Likewise, blocked `eval()` execution
will report "`eval`" as the blocked resource.
5. The `manifest-src` directive has been added.
6. The `report-uri` directive is deprecated in favor of the new `report-to`
directive, which relies on [[REPORTING]] as infrastructure.
7. The `'strict-dynamic'` source expression will now allow script which
executes on a page to load more script via non-<a>"parser-inserted"</a>
<{script}> elements. Details are in [[#strict-dynamic-usage]].
8. The `'unsafe-hashes'` source expression will now allow event
handlers, style attributes and `javascript:` navigation targets to match
hashes. Details in [[#unsafe-hashes-usage]].
9. The <a>source expression</a> matching has been changed to require explicit presence
of any non-<a>HTTP(S) scheme</a>, rather than <a>local scheme</a>,
unless that non-<a>HTTP(S) scheme</a> is the same as the scheme of protected resource,
as described in [[#match-url-to-source-expression]].
10. Hash-based source expressions may now match external scripts if the
<{script}> element that triggers the request specifies a set of integrity
metadata which is listed in the current policy. Details in
[[#external-hash]].
11. The <a>`navigate-to`</a> directive gives a resource control over the endpoints
to which it can initiate navigation.
12. Reports generated for inline violations will contain a <a for="violation">sample</a>
attribute if the relevant directive contains the <a grammar>`'report-sample'`</a>
expression.
</section>
<!-- Big Text: Framework -->
<section>
<h2 id="framework">Framework</h2>
<h3 id="framework-infrastructure">Infrastructure</h3>
This document uses ABNF grammar to specify syntax, as defined in [[!RFC5234]]. It also relies on
the `#rule` ABNF extension defined in
<a href="https://tools.ietf.org/html/rfc9110#section-5.6.1">Section 5.6.1</a> of [[!RFC9110]],
with the modification that <a grammar>OWS</a> is replaced with
<a grammar>optional-ascii-whitespace</a>. That is, the `#rule` used in this
document is defined as:
<pre>
1#element => element *( <a grammar>optional-ascii-whitespace</a> "," <a grammar>optional-ascii-whitespace</a> element )
</pre>
and for n >= 1 and m > 1:
<pre>
<n>#<m>element => element <n-1>*<m-1>( <a grammar>optional-ascii-whitespace</a> "," <a grammar>optional-ascii-whitespace</a> element )
</pre>
This document depends on the Infra Standard for a number of foundational concepts used in its
algorithms and prose [[!INFRA]].
The following definitions are used to improve readability of other definitions in this document.
<pre dfn-type="grammar" link-type="grammar">
<dfn>optional-ascii-whitespace</dfn> = *( %x09 / %x0A / %x0C / %x0D / %x20 )
<dfn>required-ascii-whitespace</dfn> = 1*( %x09 / %x0A / %x0C / %x0D / %x20 )
; These productions match the definition of <a>ASCII whitespace</a> from the <a>INFRA</a> standard.
</pre>
<h3 id="framework-policy">Policies</h3>
A <dfn export lt="content security policy object" local-lt="policy">policy</dfn> defines allowed
and restricted behaviors, and may be applied to a {{Document}}, {{WorkerGlobalScope}}, or
{{WorkletGlobalScope}}.
Each policy has an associated <dfn for="policy" export>directive set</dfn>, which is an <a>ordered
set</a> of <a>directives</a> that define the policy's implications when applied.
Each policy has an associated <dfn for="policy" export>disposition</dfn>, which is either
"`enforce`" or "`report`".
Each policy has an associated <dfn for="policy" export>source</dfn>, which is either "`header`"
or "`meta`".
Each policy has an associated <dfn for="policy" export>self-origin</dfn>, which
is an <a>origin</a> that is used when matching the <a grammar>`'self'`</a> keyword.
Note: This is needed to facilitate the <a grammar>`'self'`</a> checks of
<a>local scheme</a> documents/workers that have inherited their policy but
have an <a>opaque origin</a>. Most of the time this will simply be the
<a>environment settings object</a>'s [=environment settings object/origin=].
Multiple [=/policies=] can be applied to a single resource, and are collected into a [=list=] of
[=/policies=] known as a <dfn export>CSP list</dfn>.
A [=/CSP list=] <dfn export>contains a header-delivered Content Security Policy</dfn> if it
[=list/contains=] a [=/policy=] whose [=policy/source=] is "`header`".
A <dfn export>serialized CSP</dfn> is an <a>ASCII string</a> consisting of a semicolon-delimited
series of <a>serialized directives</a>, adhering to the following ABNF grammar [[!RFC5234]]:
<pre dfn-type="grammar" link-type="grammar">
<dfn>serialized-policy</dfn> =
<a>serialized-directive</a> *( <a>optional-ascii-whitespace</a> ";" [ <a>optional-ascii-whitespace</a> <a>serialized-directive</a> ] )
</pre>
A <dfn export>serialized CSP list</dfn> is an [=ASCII string=] consisting of a comma-delimited
series of [=serialized CSPs=], adhering to the following ABNF grammar [[!RFC5234]]:
<pre dfn-type="grammar" link-type="grammar">
<dfn>serialized-policy-list</dfn> = 1#<a>serialized-policy</a>
; The '#' rule is the one defined in section 5.6.1 of RFC 9110
; but it incorporates the modifications specified
; in section 2.1 of this document.
</pre>
<h4 id="parse-serialized-policy" algorithm>
Parse a serialized CSP
</h4>
To <dfn abstract-op>parse a serialized CSP</dfn>, given a [=string=] (|serialized|), a
[=policy/source=] (|source|), and a [=policy/disposition=] (|disposition|), execute the
following steps.
This algorithm returns a [=Content Security Policy object=]. If |serialized| could not be
parsed, the object's [=policy/directive set=] will be empty.
<ol class="algorithm">
1. Let |policy| be a new [=/policy=] with an empty [=policy/directive set=], a [=policy/source=]
of |source|, and a [=policy/disposition=] of |disposition|.
2. For each |token| returned by [=strictly split a string|strictly splitting=] |serialized| on
the U+003B SEMICOLON character (`;`):
1. [=Strip leading and trailing ASCII whitespace=] from |token|.
2. If |token| is an empty string, or if |token| is not an [=ASCII string=], [=iteration/continue=].
3. Let |directive name| be the result of [=collecting a sequence of code points=] from
|token| which are not [=ASCII whitespace=].
4. Set |directive name| to be the result of running <a>ASCII lowercase</a>
on |directive name|.
Note: Directive names are case-insensitive, that is: `script-SRC 'none'` and
`ScRiPt-sRc 'none'` are equivalent.
5. If |policy|'s [=policy/directive set=] contains a [=directive=] whose [=directive/name=]
is |directive name|, [=iteration/continue=].
Note: In this case, the user agent SHOULD notify developers that a duplicate
directive was ignored. A console warning might be appropriate, for example.
6. Let |directive value| be the result of
<a lt="split a string on ASCII whitespace">splitting |token| on
ASCII whitespace</a>.
7. Let |directive| be a new [=directive=] whose [=directive/name=] is |directive name|, and
[=directive/value=] is |directive value|.
8. [=set/append|Append=] |directive| to |policy|'s [=policy/directive set=].
3. Return |policy|.
</ol>
<h4 id="parse-serialized-policy-list" algorithm>
Parse a serialized CSP list
</h4>
To <dfn abstract-op>parse a serialized CSP list</dfn>, given a [=byte sequence=] or [=string=]
(|list|), a [=policy/source=] (|source|), and a [=policy/disposition=] (|disposition|), execute
the following steps.
This algorithm returns a [=list=] of [=Content Security Policy objects=]. If |list| cannot be
parsed, the returned list will be empty.
<ol class="algorithm">
1. If |list| is a [=byte sequence=], then set |list| to be the result of <a
lt="isomorphic decode">isomorphic decoding</a> |list|.
2. Let |policies| be an empty [=list=].
3. [=list/For each=] |token| returned by <a lt="split a string on commas">splitting |list| on commas</a>:
1. Let |policy| be the result of <a abstract-op lt="parse a serialized CSP">parsing</a>
|token|, with a [=policy/source=] of |source|, and [=policy/disposition=] of
|disposition|.
2. If |policy|'s [=policy/directive set=] is empty, [=iteration/continue=].
3. [=list/append|Append=] |policy| to |policies|.
4. Return |policies|.
</ol>
<h4 id="parse-response-csp" algorithm dfn export>
Parse |response|'s Content Security Policies
</h4>
To <dfn abstract-op>parse a response's Content Security Policies</dfn> given a <a>response</a>
(|response|):
<ol class="algorithm">
1. Let |policies| be the result of <a abstract-op lt="parse a serialized CSP list">parsing</a>
the result of [=extracting header list values=] given `Content-Security-Policy` and
|response|'s [=response/header list=], with a [=policy/source=] of "`header`", and a
[=policy/disposition=] of "`enforce`".
2. Append to |policies| the result of
<a abstract-op lt="parse a serialized CSP list">parsing</a> the result of
[=extracting header list values=] given `Content-Security-Policy-Report-Only` and
|response|'s [=response/header list=], with a [=policy/source=] of "`header`", and a
[=policy/disposition=] of "`report`".
3. For each |policy| in |policies|:
1. Set |policy|'s [=policy/self-origin=] to |response|'s [=response/url=]'s
[=url/origin=].
4. Return |policies|.
</ol>
Note: When <a abstract-op lt="parse a response's Content Security Policies">parsing a response's
Content Security Policies</a>, if the resulting |policies| end up containing at least one item,
user agents can hold a flag on |policies| and use it to optimize away the [=/contains a
header-delivered Content Security Policy=] algorithm.
<h3 id="framework-directives">Directives</h3>
Each <a for="/">policy</a> contains an <a>ordered set</a> of <dfn export>directives</dfn> (its
<a for="policy">directive set</a>), each of which controls a specific behavior. The directives
defined in this document are described in detail in [[#csp-directives]].
Each <a>directive</a> is a <dfn for="directive" export>name</dfn> /
<dfn for="directive" export>value</dfn> pair. The <a for="directive">name</a> is a
non-empty <a>string</a>, and the <a>value</a> is a <a>set</a> of non-empty <a>strings</a>. The
<a>value</a> MAY be <a for="list" lt="is empty">empty</a>.
A <dfn export>serialized directive</dfn> is an <a>ASCII string</a>, consisting of one or more
whitespace-delimited tokens, and adhering to the following ABNF [[!RFC5234]]:
<pre dfn-type="grammar" link-type="grammar">
<dfn>serialized-directive</dfn> = <a>directive-name</a> [ <a>required-ascii-whitespace</a> <a>directive-value</a> ]
<dfn>directive-name</dfn> = 1*( <a>ALPHA</a> / <a>DIGIT</a> / "-" )
<dfn>directive-value</dfn> = *( <a>required-ascii-whitespace</a> / ( %x21-%x2B / %x2D-%x3A / %x3C-%x7E ) )
; Directive values may contain whitespace and <a>VCHAR</a> characters,
; excluding ";" and ",". The second half of the definition
; above represents all <a>VCHAR</a> characters (%x21-%x7E)
; without ";" and "," (%x3B and %x2C respectively)
; <a>ALPHA</a>, <a>DIGIT</a>, and <a>VCHAR</a> are defined in Appendix B.1 of RFC 5234.
</pre>
<a>Directives</a> have a number of associated algorithms:
1. A <dfn for="directive" export>pre-request check</dfn>, which takes a
<a for="/">request</a> and a <a for="/">policy</a> as an argument, and is executed
during [[#should-block-request]]. This algorithm returns "`Allowed`" unless
otherwise specified.
2. A <dfn for="directive" export>post-request check</dfn>, which takes a
<a for="/">request</a>, a <a>response</a>, and a <a for="/">policy</a> as arguments,
and is executed during [[#should-block-response]]. This algorithm returns
"`Allowed`" unless otherwise specified.
3. An <dfn for="directive" export>inline check</dfn>, which takes an {{Element}}, a
type string, a <a for="/">policy</a>, and a source string as arguments,
and is executed during [[#should-block-inline]] and during
[[#should-block-navigation-request]] for `javascript:` requests. This
algorithm returns "`Allowed`" unless otherwise specified.
4. An <dfn for="directive" export>initialization</dfn>, which takes a {{Document}}
or <a for="/">global object</a> and a <a for="/">policy</a> as arguments. This
algorithm is executed during [[#run-document-csp-initialization]] and
[[#run-global-object-csp-initialization]]. Unless otherwise specified, it has no
effect and it returns "`Allowed`".
5. A <dfn for="directive" export>pre-navigation check</dfn>, which takes a
<a for="/">request</a>, a navigation type string ("`form-submission`"
or "`other`"), and a <a for="/">policy</a> as arguments, and
is executed during [[#should-block-navigation-request]]. It returns
"`Allowed`" unless otherwise specified.
6. A <dfn for="directive" export>navigation response check</dfn>, which takes a
<a for="/">request</a>, a navigation type string ("`form-submission`" or "`other`"),
a <a>response</a>, a <a>browsing context</a>, a check type string ("`source`"
or "`response`"), and a <a for="/">policy</a> as arguments, and is executed during
[[#should-block-navigation-response]]. It returns "`Allowed`" unless otherwise specified.
8. A <dfn for="directive" export>webrtc pre-connect check</dfn>, which takes a [=/policy=], and
is executed during [[#should-block-rtc-connection]]. It returns "`Allowed`" unless
otherwise specified.
<h4 id="framework-directive-source-list">Source Lists</h4>
Many <a>directives</a>' <a>values</a> consist of <dfn export>source lists</dfn>: <a>sets</a>
of <a>strings</a> which identify content that can be fetched and potentially embedded or
executed. Each <a>string</a> represents one of the following types of <dfn export>source
expression</dfn>:
1. Keywords such as <a grammar>`'none'`</a> and
<a grammar>`'self'`</a> (which match nothing and the current
URL's origin, respectively)
2. Serialized URLs such as `https://example.com/path/to/file.js`
(which matches a specific file) or `https://example.com/`
(which matches everything on that origin)
3. Schemes such as `https:` (which matches any resource having
the specified scheme)
4. Hosts such as `example.com` (which matches any resource on
the host, regardless of scheme) or `*.example.com` (which
matches any resource on the host's subdomains (and any of
its subdomains' subdomains, and so on))
5. Nonces such as `'nonce-ch4hvvbHDpv7xCSvXCs3BrNggHdTzxUA'` (which can match
specific elements on a page)
6. Digests such as `'sha256-abcd...'` (which can match specific
elements on a page)
A <dfn export>serialized source list</dfn> is an <a>ASCII string</a>, consisting of a
whitespace-delimited series of <a>source expressions</a>, adhering to the following ABNF grammar
[[!RFC5234]]:
<pre dfn-type="grammar" link-type="grammar">
<dfn>serialized-source-list</dfn> = ( <a>source-expression</a> *( <a>required-ascii-whitespace</a> <a>source-expression</a> ) ) / "<dfn>'none'</dfn>"
<dfn>source-expression</dfn> = <a>scheme-source</a> / <a>host-source</a> / <a>keyword-source</a>
/ <a>nonce-source</a> / <a>hash-source</a>
; Schemes: "https:" / "custom-scheme:" / "another.custom-scheme:"
<dfn>scheme-source</dfn> = <a>scheme-part</a> ":"
; Hosts: "example.com" / "*.example.com" / "https://*.example.com:12/path/to/file.js"
<dfn>host-source</dfn> = [ <a>scheme-part</a> "://" ] <a>host-part</a> [ ":" <a>port-part</a> ] [ <a>path-part</a> ]
<dfn>scheme-part</dfn> = <a>scheme</a>
; <a>scheme</a> is defined in section 3.1 of RFC 3986.
<dfn>host-part</dfn> = "*" / [ "*." ] 1*<a>host-char</a> *( "." 1*<a>host-char</a> )
<dfn>host-char</dfn> = <a>ALPHA</a> / <a>DIGIT</a> / "-"
<dfn>port-part</dfn> = 1*<a>DIGIT</a> / "*"
<dfn>path-part</dfn> = <a>path-absolute</a> (but not including ";" or ",")
; <a>path-absolute</a> is defined in section 3.3 of RFC 3986.
; Keywords:
<dfn>keyword-source</dfn> = "<dfn>'self'</dfn>" / "<dfn>'unsafe-inline'</dfn>" / "<dfn>'unsafe-eval'</dfn>"
/ "<dfn>'strict-dynamic'</dfn>" / "<dfn>'unsafe-hashes'</dfn>" /
/ "<dfn>'report-sample'</dfn>" / "<dfn>'unsafe-allow-redirects'</dfn>"
/ "<dfn>'wasm-unsafe-eval'</dfn>"
ISSUE: Bikeshed `unsafe-allow-redirects`.
; Nonces: 'nonce-[nonce goes here]'
<dfn>nonce-source</dfn> = "'nonce-" <a>base64-value</a> "'"
<dfn>base64-value</dfn> = 1*( <a>ALPHA</a> / <a>DIGIT</a> / "+" / "/" / "-" / "_" )*2( "=" )
; Digests: 'sha256-[digest goes here]'
<dfn>hash-source</dfn> = "'" <a>hash-algorithm</a> "-" <a>base64-value</a> "'"
<dfn>hash-algorithm</dfn> = "sha256" / "sha384" / "sha512"
</pre>
The <a grammar>host-char</a> production intentionally contains only ASCII
characters; internationalized domain names cannot be entered directly as part
of a <a>serialized CSP</a>, but instead MUST be Punycode-encoded
[[!RFC3492]]. For example, the domain `üüüüüü.de` MUST be represented as
`xn--tdaaaaaa.de`.
Note: Though IP address do match the grammar above, only
`127.0.0.1` will actually match a URL when used in a source
expression (see [[#match-url-to-source-list]] for details). The security
properties of IP addresses are suspect, and authors ought to prefer hostnames
whenever possible.
Note: The <a grammar>base64-value</a> grammar allows both [=base64 encoding|base64=] and
[=base64url encoding|base64url=] encoding. These encodings are treated as equivalant when
processing <a grammar>hash-source</a> values. Nonces, however, are strict string matches:
we use the <a grammar>base64-value</a> grammar to limit the characters available, and
reduce the complexity for the server-side operator (encodings, etc), but the user agent
doesn't actually care about any underlying value, nor does it do any decoding of the
<a grammar>nonce-source</a> value.
<h3 id="framework-violation">Violations</h3>
A <dfn export>violation</dfn> represents an action or resource which goes against the
set of <a for="/">policy</a> objects associated with a <a for="/">global object</a>.
Each <a>violation</a> has a
<dfn for="violation" id="violation-global-object" export>global object</dfn>, which
is the <a for="/">global object</a> whose <a for="/">policy</a> has been violated.
Each <a>violation</a> has a <dfn for="violation" id="violation-url" export>url</dfn>
which is its <a for="violation">global object</a>'s {{URL}}.
Each <a>violation</a> has a
<dfn for="violation" id="violation-status" export>status</dfn> which is a
non-negative integer representing the HTTP status code of the resource for
which the global object was instantiated.
Each <a>violation</a> has a
<dfn for="violation" id="violation-resource" export>resource</dfn>, which is
either `null`, "`inline`", "`eval`", "`wasm-eval`", or a {{URL}}. It represents the resource
which violated the policy.
Note: The value `null` for a <a>violation</a>'s <a
for="violation">resource</a> is only allowed while the <a>violation</a> is
being populated. By the time the <a>violation</a> is reported and its <a
for="violation">resource</a> is used for
[[#obtain-violation-blocked-uri|obtaining the blocked URI]], the
<a>violation</a>'s <a for="violation">resource</a> should be populated with a
{{URL}} or one of the allowed strings.
Each <a>violation</a> has a
<dfn for="violation" id="violation-referrer" export>referrer</dfn>, which is either
`null`, or a {{URL}}. It represents the referrer of the resource whose policy
was violated.
Each <a>violation</a> has a
<dfn for="violation" id="violation-policy" export>policy</dfn>, which is the
<a for="/">policy</a> that has been violated.
Each <a>violation</a> has a
<dfn for="violation" id="violation-disposition" export>disposition</dfn>, which is the
<a for="policy">disposition</a> of the <a for="/">policy</a> that has been violated.
Each <a>violation</a> has an
<dfn for="violation" id="violation-effective-directive" export>effective directive</dfn>
which is a non-empty string representing the <a>directive</a> whose
enforcement caused the violation.
Each <a>violation</a> has a
<dfn for="violation" id="violation-source-file" export>source file</dfn>, which is
either `null` or a {{URL}}.
Each <a>violation</a> has a
<dfn for="violation" id="violation-line-number" export>line number</dfn>, which is
a non-negative integer.
Each <a>violation</a> has a
<dfn for="violation" id="violation-column-number" export>column number</dfn>, which
is a non-negative integer.
Each <a>violation</a> has a
<dfn for="violation" id="violation-element" export>element</dfn>, which is either
`null` or an element.
Each <a>violation</a> has a <dfn for="violation" id="violation-sample" export>sample</dfn>,
which is a string. It is the empty string unless otherwise specified.
Note: A <a>violation</a>'s <a for="violation">sample</a> will be populated with the first 40
characters of an inline script, event handler, or style that caused an violation. Violations
which stem from an external file will not include a sample in the violation report.
<h4 id="create-violation-for-global" algorithm>
Create a violation object for |global|, |policy|, and |directive|
</h4>
Given a <a for="/">global object</a> (|global|), a <a for="/">policy</a> (|policy|), and a
<a>string</a> (|directive|), the following algorithm creates a new <a>violation</a>
object, and populates it with an initial set of data:
1. Let |violation| be a new <a>violation</a> whose <a for="violation">global
object</a> is |global|, <a for="violation">policy</a> is |policy|,
<a for="violation">effective directive</a> is |directive|, and
<a for="violation">resource</a> is `null`.
2. If the user agent is currently executing script, and can extract a source
file's URL, line number, and column number from the |global|, set
|violation|'s <a for="violation">source file</a>, <a for="violation">line
number</a>, and <a for="violation">column number</a> accordingly.
ISSUE: Is this kind of thing specified anywhere? I didn't see anything
that looked useful in [[ECMA262]].
Note: User agents need to ensure that the [=violation/source file=] is the URL requested by
the page, pre-redirects. If that's not possible, user agents need to strip the URL down to an
origin to avoid unintentional leakage.
3. If |global| is a {{Window}} object, set |violation|'s
<a for="violation">referrer</a> to |global|'s {{Window/document}}'s
{{Document/referrer}}.
4. Set |violation|'s <a for="violation">status</a> to the HTTP status code
for the resource associated with |violation|'s <a for="violation">global
object</a>.
ISSUE: How, exactly, do we get the status code? We don't actually store it
anywhere.
5. Return |violation|.
<h4 id="create-violation-for-request" algorithm>
Create a violation object for |request|, and |policy|.
</h4>
Given a <a for="/">request</a> (|request|), a <a for="/">policy</a> (|policy|),
the following algorithm creates a new <a>violation</a> object,
and populates it with an initial set of data:
1. Let |directive| be the result of executing [[#effective-directive-for-a-request]]
on |request|.
2. Let |violation| be the result of executing
[[#create-violation-for-global]] on |request|'s
<a for="request">client</a>'s <a for="environment settings object">global object</a>,
|policy|, and |directive|.
3. Set |violation|'s <a for="violation">resource</a> to |request|'s
<a for="request">url</a>.
Note: We use |request|'s <a for="request">url</a>, and <em>not</em> its
<a for="request">current url</a>, as the latter might contain information
about redirect targets to which the page MUST NOT be given access.
4. Return |violation|.
</section>
<!-- Big Text: Delivery -->
<section>
<h2 id="policy-delivery">
Policy Delivery
</h2>
A server MAY declare a <a for="/">policy</a> for a particular <a>resource
representation</a> via an HTTP response header field whose value is a
<a>serialized CSP</a>. This mechanism is defined in detail in
[[#csp-header]] and [[#cspro-header]], and the integration with Fetch
and HTML is described in [[#fetch-integration]] and [[#html-integration]].
A <a for="/">policy</a> may also be declared inline in an HTML document via a
<{meta}> element's <{meta/http-equiv}> attribute, as described in
[[#meta-element]].
<h3 id="csp-header">
The `Content-Security-Policy` HTTP Response Header Field
</h3>
The <dfn export id="header-content-security-policy" http-header>`Content-Security-Policy`</dfn>
HTTP response header field is the preferred mechanism for delivering a policy from a server to a
client. The header's value is represented by the following ABNF [[!RFC5234]]:
<pre>
Content-Security-Policy = 1#<a grammar>serialized-policy</a>
; The '#' rule is the one defined in section 5.6.1 of RFC 9110
; but it incorporates the modifications specified
; in section 2.1 of this document.
</pre>
<div class="example">
<pre>
<a http-header>Content-Security-Policy</a>: script-src 'self';
report-to csp-reporting-endpoint
</pre>
</div>
A server MAY send different `Content-Security-Policy` header field
values with different <a>representations</a> of the same resource.
A server SHOULD NOT send more than one HTTP response header field named
"`Content-Security-Policy`" with a given <a>resource
representation</a>.
When the user agent receives a `Content-Security-Policy` header field, it
MUST <a abstract-op lt="parse a serialized CSP">parse</a> and <a>enforce</a> each
<a>serialized CSP</a> it contains as described in [[#fetch-integration]],
[[#html-integration]].
<h3 id="cspro-header">
The `Content-Security-Policy-Report-Only` HTTP Response Header Field
</h3>
The <dfn export id="header-content-security-policy-report-only" http-header>`Content-Security-Policy-Report-Only`</dfn>
HTTP response header field allows web developers to experiment with policies by monitoring (but
not enforcing) their effects. The header's value is represented by the following ABNF
[[!RFC5234]]:
<pre>
Content-Security-Policy-Report-Only = 1#<a grammar>serialized-policy</a>
; The '#' rule is the one defined in section 5.6.1 of RFC 9110
; but it incorporates the modifications specified
; in section 2.1 of this document.
</pre>
This header field allows developers to piece together their security policy in
an iterative fashion, deploying a report-only policy based on their best
estimate of how their site behaves, watching for violation reports, and then
moving to an enforced policy once they've gained confidence in that behavior.
<div class="example">
<pre>
<a http-header>Content-Security-Policy-Report-Only</a>: script-src 'self';
report-to csp-reporting-endpoint
</pre>
</div>
A server MAY send different `Content-Security-Policy-Report-Only`
header field values with different <a>representations</a> of the same
resource.
A server SHOULD NOT send more than one HTTP response header field named
"`Content-Security-Policy-Report-Only`" with a given <a>resource
representation</a>.
When the user agent receives a `Content-Security-Policy-Report-Only` header
field, it MUST <a abstract-op lt="parse a serialized CSP">parse</a> and <a>monitor</a>
each <a>serialized CSP</a> it contains as described in
[[#fetch-integration]] and [[#html-integration]].
Note: The <a http-header>`Content-Security-Policy-Report-Only`</a> header is
<strong>not</strong> supported inside a <{meta}> element.
<h3 id="meta-element">
The `<meta>` element
</h3>
A {{Document}} may deliver a policy via one or more HTML <{meta}> elements
whose <{meta/http-equiv}> attributes are an <a>ASCII case-insensitive</a>
match for the string "`Content-Security-Policy`". For example:
<div class="example">
<pre highlight="html">
<meta http-equiv="Content-Security-Policy" content="script-src 'self'">
</pre>
</div>
Implementation details can be found in HTML's <a>Content Security Policy
state</a> `http-equiv` processing instructions [[!HTML]].
Note: The <a http-header>`Content-Security-Policy-Report-Only`</a> header is <em>not</em>
supported inside a <{meta}> element. Neither are the `report-uri`,
`frame-ancestors`, and `sandbox` directives.
Authors are <em>strongly encouraged</em> to place <{meta}> elements as early
in the document as possible, because policies in <{meta}> elements are not
applied to content which precedes them. In particular, note that resources
fetched or prefetched using the `Link` HTTP response header
field, and resources fetched or prefetched using <{link}> and <{script}>
elements which precede a <{meta}>-delivered policy will not be blocked.
Note: A policy specified via a <{meta}> element will be enforced along with
any other policies active for the protected resource, regardless
of where they're specified. The general impact of enforcing multiple
policies is described in [[#multiple-policies]].
Note: Modifications to the <{meta/content}> attribute of a <{meta}> element
after the element has been parsed will be ignored.
</section>
<!-- Big Text: Integration -->
<section>
<h2 id="integrations">Integrations</h2>