index.md

---

title: "CSP: base-uri"
slug: Web/HTTP/Headers/Content-Security-Policy/base-uri
browser-compat: http.headers.Content-Security-Policy.base-uri

---

{{HTTPSidebar}}

The HTTP {{HTTPHeader("Content-Security-Policy")}} base-uri directive restricts the URLs which can be used in a document's {{HTMLElement("base")}} element. If this value is absent, then any URI is allowed. If this directive is absent, the user agent will use the value in the {{HTMLElement("base")}} element.

CSP version	2
Directive type	{{Glossary("Document directive")}}
{{CSP("default-src")}} fallback	No. Not setting this allows any URL.

Syntax

One or more sources can be allowed for the base-uri policy:

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

Sources

This directive uses most of the same source values for arguments as other CSP directives: CSP Source Values.

Note however that some of the values don't make sense for base-uri, such as the keywords 'unsafe-inline' and 'strict-dynamic'.

Examples

Meta tag configuration

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

Apache configuration

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

Nginx configuration

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

Violation case

Since your domain isn't example.com, a {{HTMLElement("base")}} element with its href set to https://example.com will result in a CSP violation.

<meta http-equiv="Content-Security-Policy" content="base-uri 'self'" />
<base href="https://example.com/" />

<!--
// Error: Refused to set the document's base URI to 'https://example.com/'
// because it violates the following Content Security Policy
// directive: "base-uri 'self'"
-->

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

See also

• {{HTTPheader("Content-Security-Policy")}}

• {{HTMLElement("base")}}

• {{domxref("Node.baseURI")}}