The HTTP Permissions-Policy header loopback-network directive controls whether the current document is allowed to make network requests to loopback addresses.

A loopback address is only accessible on the local host; its target will differ on every device. For example, 127.0.0.1, which is generally known as localhost.

Specifically, where a defined policy blocks use of this feature, requests to loopback addresses will always fail.

See Local Network Access for more details.

Syntax

Permissions-Policy: loopback-network=<allowlist>;

<allowlist>

A list of origins for which permission is granted to use the feature. See Permissions-Policy > Syntax for more details.

Default policy

The default allowlist for loopback-network is self. The top-level browsing context and same-origin iframes are allowed access to the loopback-network feature by default.

Examples

Basic usage

SecureCorp Inc. wants to disallow loopback-network within all cross-origin iframes except those whose origin is https://example.com. It can do so by delivering the following HTTP response header to define a Permissions Policy:

Permissions-Policy: loopback-network=(self "https://example.com")

SecureCorp Inc. must also include an allow attribute on each <iframe> element where loopback-network is to be allowed:

<iframe src="https://example.com/lna" allow="loopback-network"></iframe>

Using the default policy

If an allowlist for loopback-network is not defined by a Permissions-Policy response header, user agents will apply the default allowlist self. In this mode, loopback-network is automatically allowed in the top-level browsing context and same-origin iframes, but not in cross-origin iframes.

To allow loopback-network in a cross-origin iframe, include an allow attribute on the <iframe> element:

<iframe src="https://other.com/lna" allow="loopback-network"></iframe>

Specifications

Browser compatibility

See also

• Local Network Access
• Permissions-Policy header
• Permissions Policy