CSP: script-src

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HTTP の Content-Security-Policy (CSP) script-src ディレクティブは、 JavaScript の情報なソースを指定します。これは <script> 要素の中に直接読み込まれる URL だけでなく、インラインのスクリプトイベントハンドラー (onclick) やスクリプト実行のトリガーとなりうる XSLT スタイルシートのようなものも含まれます。

CSP バージョン 1
ディレクティブ種別 フェッチディレクティブ
default-src フォールバック あり。このディレクティブがない場合、ユーザーエージェントは default-src ディレクティブを探します。

構文

script-src ポリシーには、１つまたは複数のソースが許可されています。

Content-Security-Policy: script-src <source>;
Content-Security-Policy: script-src <source> <source>;

ソース

<source> can be one of the following:

<host-source>
Internet hosts by name or IP address, as well as an optional URL scheme and/or port number. The site's address may include an optional leading wildcard (the asterisk character, '*'), and you may use a wildcard (again, '*') as the port number, indicating that all legal ports are valid for the source.
Examples:
  • http://*.example.com: Matches all attempts to load from any subdomain of example.com using the http: URL scheme.
  • mail.example.com:443: Matches all attempts to access port 443 on mail.example.com.
  • https://store.example.com: Matches all attempts to access store.example.com using https:.
<scheme-source>
A schema such as 'http:' or 'https:'. The colon is required, single quotes shouldn't be used. You can also specify data schemas (not recommended).
  • data: Allows data: URIs to be used as a content source. This is insecure; an attacker can also inject arbitrary data: URIs. Use this sparingly and definitely not for scripts.
  • mediastream: Allows mediastream: URIs to be used as a content source.
  • blob: Allows blob: URIs to be used as a content source.
  • filesystem: Allows filesystem: URIs to be used as a content source.
'self'
Refers to the origin from which the protected document is being served, including the same URL scheme and port number. You must include the single quotes. Some browsers specifically exclude blob and filesystem from source directives. Sites needing to allow these content types can specify them using the Data attribute.
'unsafe-eval'
Allows the use of eval() and similar methods for creating code from strings. You must include the single quotes.
'unsafe-hashes'
Allows to enable specific inline event handlers. If you only need to allow inline event handlers and not inline <script> elements or javascript: URLs, this is a safer method compared to using the unsafe-inline expression.
'unsafe-inline'
Allows the use of inline resources, such as inline <script> elements, javascript: URLs, inline event handlers, and inline <style> elements. You must include the single quotes.
'none'
Refers to the empty set; that is, no URLs match. The single quotes are required.
'nonce-<base64-value>'
A whitelist for specific inline scripts using a cryptographic nonce (number used once). The server must generate a unique nonce value each time it transmits a policy. It is critical to provide an unguessable nonce, as bypassing a resource’s policy is otherwise trivial. See unsafe inline script for an example. Specifying nonce makes a modern browser ignore 'unsafe-inline' which could still be set for older browsers without nonce support.
'<hash-algorithm>-<base64-value>'
A sha256, sha384 or sha512 hash of scripts or styles. The use of this source consists of two portions separated by a dash: the encryption algorithm used to create the hash and the base64-encoded hash of the script or style. When generating the hash, don't include the <script> or <style> tags and note that capitalization and whitespace matter, including leading or trailing whitespace. See unsafe inline script for an example. In CSP 2.0 this applied only to inline scripts. CSP 3.0 allows it in the case of script-src for external scripts.
'strict-dynamic'
The strict-dynamic source expression specifies that the trust explicitly given to a script present in the markup, by accompanying it with a nonce or a hash, shall be propagated to all the scripts loaded by that root script. At the same time, any whitelist or source expressions such as 'self' or 'unsafe-inline' will be ignored. See script-src for an example.
'report-sample'
Requires a sample of the violating code to be included in the violation report.

例

違反例

この CSP ヘッダーがある場合、

Content-Security-Policy: script-src https://example.com/

以下のスクリプトはブロックされ、読み込みや実行が行われません。

<script src="https://not-example.com/js/library.js"></script>

なお、インラインのイベントハンドラーも同様にブロックされます。

<button id="btn" onclick="doSomething()">

これを addEventListener の呼び出しに置き換えてください。

document.getElementById("btn").addEventListener('click', doSomething);

安全ではないインラインのスクリプト

Note: Disallowing inline styles and inline scripts is one of the biggest security wins CSP provides. However, if you absolutely have to use it, there are a few mechanisms that will allow them.

To allow inline scripts and inline event handlers, 'unsafe-inline', a nonce-source or a hash-source that matches the inline block can be specified.

Content-Security-Policy: script-src 'unsafe-inline';

The above Content Security Policy will allow inline <script> elements

<script> 
  var inline = 1; 
</script>

You can use a nonce-source to only allow specific inline script blocks:

Content-Security-Policy: script-src 'nonce-2726c7f26c'

You will have to set the same nonce on the <script> element:

<script nonce="2726c7f26c">
  var inline = 1;
</script>

Alternatively, you can create hashes from your inline scripts. CSP supports sha256, sha384 and sha512.

Content-Security-Policy: script-src 'sha256-B2yPHKaXnvFWtRChIbabYmUBFZdVfKKXHbWtWidDVF8='

When generating the hash, don't include the <script> tags and note that capitalization and whitespace matter, including leading or trailing whitespace.

<script>var inline = 1;</script>

Unsafe eval expressions

The 'unsafe-eval' source expression controls several script execution methods that create code from strings. If 'unsafe-eval' isn't specified with the script-src directive, the following methods are blocked and won't have any effect:

strict-dynamic

The 'strict-dynamic' source expression specifies that the trust explicitly given to a script present in the markup, by accompanying it with a nonce or a hash, shall be propagated to all the scripts loaded by that root script. At the same time, any whitelist or source expressions such as 'self' or 'unsafe-inline' will be ignored. For example, a policy such as script-src 'strict-dynamic' 'nonce-R4nd0m' https://whitelisted.com/ would allow loading of a root script with <script nonce="R4nd0m" src="https://example.com/loader.js"> and propagate that trust to any script loaded by loader.js, but disallow loading scripts from https://whitelisted.com/ unless accompanied by a nonce or loaded from a trusted script.

script-src 'strict-dynamic' 'nonce-someNonce'

Or

script-src 'strict-dynamic' 'sha256-base64EncodedHash'

It is possible to deploy strict-dynamic in a backwards compatible way, without requiring user-agent sniffing.
The policy:

script-src 'unsafe-inline' https: 'nonce-abcdefg' 'strict-dynamic'

will act like'unsafe-inline' https: in browsers that support CSP1, https: 'nonce-abcdefg' in browsers that support CSP2, and 'nonce-abcdefg' 'strict-dynamic' in browsers that support CSP3.

仕様書

仕様書 状態 備考
Content Security Policy Level 3
script-src の定義		 草案 変更なし
Content Security Policy Level 2
script-src の定義		 勧告 初回定義

ブラウザーの対応

No compatibility data found. Please contribute data for "http.headers.csp.script-src" (depth: 1) to the MDN compatibility data repository.

関連情報