CSP: base-uri

HTTP 协议 Content-Security-Policy 首部字段中的 base-uri 指令限制了可以应用于一个文档的 <base> 元素的 URL。假如指令值为空，那么任何 URL 都是允许的。如果指令不存在，那么用户代理会使用 <base> 元素中的值。 

语法

base-uri 安全策略可以设置一个或多个源：

Content-Security-Policy: base-uri <source>;
Content-Security-Policy: base-uri <source> <source>;

源

<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-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.

'unsafe-eval'

Allows the use of eval() and similar methods for creating code from strings. 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.

<hash-source>

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.

示例

Meta tag 配置

<meta http-equiv="Content-Security-Policy" content="base-uri 'self'">

Apache 配置

<IfModule mod_headers.c>
Header set Content-Security-Policy "base-uri 'self';
</IfModule>

Nginx 配置

add_header Content-Security-Policy "base-uri 'self';"

违犯策略的案例

假如你的域名不是 example.com，那么将 <base> 元素的 href 属性值设置成 example.com 会违犯 CSP 策略。

<meta http-equiv="Content-Security-Policy" content="base-uri 'self'">
<base href="http://example.com/">
// Error: Refused to set the document's base URI to 'http://example.com/'
// because it violates the following Content Security Policy
// directive: "base-uri 'self'"

规范

浏览器兼容性

The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.

相关内容

• Content-Security-Policy
• <base>
• Node.baseURI